perf/x86/intel: Rename DMR offcore_rsp attribute to offmodule_rspgrafted

DMR introduces Offmodule Response events in place of the legacy
Offcore Response events, but it still exposes the inherited
offcore_rsp PMU attribute for programming the corresponding MSR data.

Rename the DMR PMU attribute to offmodule_rsp so the sysfs interface
matches the underlying event name and avoids user & tooling confusion.

Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20260917015234.981153-12-dapeng1.mi@linux.intel.com

20 files changed, 4971 insertions, 0 deletions

diff --git a/drivers/block/zram/Kconfig b/drivers/block/zram/Kconfig
new file mode 100644
index 000000000..402b7b175
--- /dev/null
+++ b/drivers/block/zram/Kconfig
@@ -0,0 +1,147 @@
+# SPDX-License-Identifier: GPL-2.0
+config ZRAM
+	tristate "Compressed RAM block device support"
+	depends on BLOCK && SYSFS && MMU
+	select ZSMALLOC
+	help
+	  Creates virtual block devices called /dev/zramX (X = 0, 1, ...).
+	  Pages written to these disks are compressed and stored in memory
+	  itself. These disks allow very fast I/O and compression provides
+	  good amounts of memory savings.
+
+	  It has several use cases, for example: /tmp storage, use as swap
+	  disks and maybe many more.
+
+	  See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_BACKEND_LZ4
+	bool "lz4 compression support"
+	depends on ZRAM
+	select LZ4_COMPRESS
+	select LZ4_DECOMPRESS
+
+config ZRAM_BACKEND_LZ4HC
+	bool "lz4hc compression support"
+	depends on ZRAM
+	select LZ4HC_COMPRESS
+	select LZ4_DECOMPRESS
+
+config ZRAM_BACKEND_ZSTD
+	bool "zstd compression support"
+	depends on ZRAM
+	select ZSTD_COMPRESS
+	select ZSTD_DECOMPRESS
+
+config ZRAM_BACKEND_DEFLATE
+	bool "deflate compression support"
+	depends on ZRAM
+	select ZLIB_DEFLATE
+	select ZLIB_INFLATE
+
+config ZRAM_BACKEND_842
+	bool "842 compression support"
+	depends on ZRAM
+	select 842_COMPRESS
+	select 842_DECOMPRESS
+
+config ZRAM_BACKEND_FORCE_LZO
+	depends on ZRAM
+	def_bool !ZRAM_BACKEND_LZ4 && !ZRAM_BACKEND_LZ4HC && \
+		!ZRAM_BACKEND_ZSTD && !ZRAM_BACKEND_DEFLATE && \
+		!ZRAM_BACKEND_842
+
+config ZRAM_BACKEND_LZO
+	bool "lzo and lzo-rle compression support" if !ZRAM_BACKEND_FORCE_LZO
+	depends on ZRAM
+	default ZRAM_BACKEND_FORCE_LZO
+	select LZO_COMPRESS
+	select LZO_DECOMPRESS
+
+choice
+	prompt "Default zram compressor"
+	default ZRAM_DEF_COMP_LZORLE
+	depends on ZRAM
+
+config ZRAM_DEF_COMP_LZORLE
+	bool "lzo-rle"
+	depends on ZRAM_BACKEND_LZO
+
+config ZRAM_DEF_COMP_LZO
+	bool "lzo"
+	depends on ZRAM_BACKEND_LZO
+
+config ZRAM_DEF_COMP_LZ4
+	bool "lz4"
+	depends on ZRAM_BACKEND_LZ4
+
+config ZRAM_DEF_COMP_LZ4HC
+	bool "lz4hc"
+	depends on ZRAM_BACKEND_LZ4HC
+
+config ZRAM_DEF_COMP_ZSTD
+	bool "zstd"
+	depends on ZRAM_BACKEND_ZSTD
+
+config ZRAM_DEF_COMP_DEFLATE
+	bool "deflate"
+	depends on ZRAM_BACKEND_DEFLATE
+
+config ZRAM_DEF_COMP_842
+	bool "842"
+	depends on ZRAM_BACKEND_842
+
+endchoice
+
+config ZRAM_DEF_COMP
+	string
+	depends on ZRAM
+	default "lzo-rle" if ZRAM_DEF_COMP_LZORLE
+	default "lzo" if ZRAM_DEF_COMP_LZO
+	default "lz4" if ZRAM_DEF_COMP_LZ4
+	default "lz4hc" if ZRAM_DEF_COMP_LZ4HC
+	default "zstd" if ZRAM_DEF_COMP_ZSTD
+	default "deflate" if ZRAM_DEF_COMP_DEFLATE
+	default "842" if ZRAM_DEF_COMP_842
+	default "unset-value"
+
+config ZRAM_WRITEBACK
+       bool "Write back incompressible or idle page to backing device"
+       depends on ZRAM
+       help
+	 This lets zram entries (incompressible or idle pages) be written
+	 back to a backing device, helping save memory.
+	 For this feature, admin should set up backing device via
+	 /sys/block/zramX/backing_dev.
+
+	 With /sys/block/zramX/{idle,writeback}, application could ask
+	 idle page's writeback to the backing device to save in memory.
+
+	 See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_TRACK_ENTRY_ACTIME
+	bool "Track access time of zram entries"
+	depends on ZRAM
+	help
+	  With this feature zram tracks access time of every stored
+	  entry (page), which can be used for a more fine grained IDLE
+	  pages writeback.
+
+config ZRAM_MEMORY_TRACKING
+	bool "Track zRam block status"
+	depends on ZRAM && DEBUG_FS
+	select ZRAM_TRACK_ENTRY_ACTIME
+	help
+	  With this feature, admin can track the state of allocated blocks
+	  of zRAM. Admin could see the information via
+	  /sys/kernel/debug/zram/zramX/block_state.
+
+	  See Documentation/admin-guide/blockdev/zram.rst for more information.
+
+config ZRAM_MULTI_COMP
+	bool "Enable multiple compression streams"
+	depends on ZRAM
+	help
+	  This will enable multi-compression streams, so that ZRAM can
+	  re-compress pages using a potentially slower but more effective
+	  compression algorithm. Note, that IDLE page recompression
+	  requires ZRAM_TRACK_ENTRY_ACTIME.
diff --git a/drivers/block/zram/Makefile b/drivers/block/zram/Makefile
new file mode 100644
index 000000000..0fdefd576
--- /dev/null
+++ b/drivers/block/zram/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+zram-y	:=	zcomp.o zram_drv.o
+
+zram-$(CONFIG_ZRAM_BACKEND_LZO)		+= backend_lzorle.o backend_lzo.o
+zram-$(CONFIG_ZRAM_BACKEND_LZ4)		+= backend_lz4.o
+zram-$(CONFIG_ZRAM_BACKEND_LZ4HC)	+= backend_lz4hc.o
+zram-$(CONFIG_ZRAM_BACKEND_ZSTD)	+= backend_zstd.o
+zram-$(CONFIG_ZRAM_BACKEND_DEFLATE)	+= backend_deflate.o
+zram-$(CONFIG_ZRAM_BACKEND_842)		+= backend_842.o
+
+obj-$(CONFIG_ZRAM)	+=	zram.o
diff --git a/drivers/block/zram/backend_842.c b/drivers/block/zram/backend_842.c
new file mode 100644
index 000000000..3846a04c6
--- /dev/null
+++ b/drivers/block/zram/backend_842.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "842: " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/sw842.h>
+#include <linux/vmalloc.h>
+
+#include "backend_842.h"
+
+static void release_params_842(struct zcomp_params *params)
+{
+}
+
+static int setup_params_842(struct zcomp_params *params)
+{
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	if (params->level != ZCOMP_PARAM_NOT_SET) {
+		pr_err("compression level is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+static void destroy_842(struct zcomp_ctx *ctx)
+{
+	kfree(ctx->context);
+}
+
+static int create_842(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	ctx->context = kmalloc(SW842_MEM_COMPRESS, GFP_KERNEL);
+	if (!ctx->context)
+		return -ENOMEM;
+	return 0;
+}
+
+static int compress_842(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			struct zcomp_req *req)
+{
+	unsigned int dlen = req->dst_len;
+	int ret;
+
+	ret = sw842_compress(req->src, req->src_len, req->dst, &dlen,
+			     ctx->context);
+	if (ret == 0)
+		req->dst_len = dlen;
+	return ret;
+}
+
+static int decompress_842(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			  struct zcomp_req *req)
+{
+	unsigned int dlen = req->dst_len;
+
+	return sw842_decompress(req->src, req->src_len, req->dst, &dlen);
+}
+
+const struct zcomp_ops backend_842 = {
+	.compress	= compress_842,
+	.decompress	= decompress_842,
+	.create_ctx	= create_842,
+	.destroy_ctx	= destroy_842,
+	.setup_params	= setup_params_842,
+	.release_params	= release_params_842,
+	.name		= "842",
+};
diff --git a/drivers/block/zram/backend_842.h b/drivers/block/zram/backend_842.h
new file mode 100644
index 000000000..4dc85c188
--- /dev/null
+++ b/drivers/block/zram/backend_842.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_842_H__
+#define __BACKEND_842_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_842;
+
+#endif /* __BACKEND_842_H__ */
diff --git a/drivers/block/zram/backend_deflate.c b/drivers/block/zram/backend_deflate.c
new file mode 100644
index 000000000..f71b11bca
--- /dev/null
+++ b/drivers/block/zram/backend_deflate.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "deflate: " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+
+#include "backend_deflate.h"
+
+/* Use the same value as crypto API */
+#define DEFLATE_DEF_WINBITS		(-11)
+#define DEFLATE_DEF_MEMLEVEL		MAX_MEM_LEVEL
+
+struct deflate_ctx {
+	struct z_stream_s cctx;
+	struct z_stream_s dctx;
+};
+
+static void deflate_release_params(struct zcomp_params *params)
+{
+}
+
+static int deflate_setup_params(struct zcomp_params *params)
+{
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
+		params->level = Z_DEFAULT_COMPRESSION;
+	} else if (params->level < Z_DEFAULT_COMPRESSION ||
+		   params->level > Z_BEST_COMPRESSION) {
+		pr_err("invalid compression level %d\n", params->level);
+		return -EINVAL;
+	}
+
+	if (params->deflate.winbits == ZCOMP_PARAM_NOT_SET) {
+		params->deflate.winbits = DEFLATE_DEF_WINBITS;
+	} else {
+		s32 wb = params->deflate.winbits;
+
+		if ((wb < -15 || wb > -9) && (wb < 9 || wb > 15)) {
+			pr_err("invalid winbits %d\n", wb);
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static void deflate_destroy(struct zcomp_ctx *ctx)
+{
+	struct deflate_ctx *zctx = ctx->context;
+
+	if (!zctx)
+		return;
+
+	if (zctx->cctx.workspace) {
+		zlib_deflateEnd(&zctx->cctx);
+		vfree(zctx->cctx.workspace);
+	}
+	if (zctx->dctx.workspace) {
+		zlib_inflateEnd(&zctx->dctx);
+		vfree(zctx->dctx.workspace);
+	}
+	kfree(zctx);
+}
+
+static int deflate_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	struct deflate_ctx *zctx;
+	size_t sz;
+	int ret;
+
+	zctx = kzalloc_obj(*zctx);
+	if (!zctx)
+		return -ENOMEM;
+
+	ctx->context = zctx;
+	sz = zlib_deflate_workspacesize(params->deflate.winbits, MAX_MEM_LEVEL);
+	zctx->cctx.workspace = vzalloc(sz);
+	if (!zctx->cctx.workspace)
+		goto error;
+
+	ret = zlib_deflateInit2(&zctx->cctx, params->level, Z_DEFLATED,
+				params->deflate.winbits, DEFLATE_DEF_MEMLEVEL,
+				Z_DEFAULT_STRATEGY);
+	if (ret != Z_OK)
+		goto error;
+
+	sz = zlib_inflate_workspacesize();
+	zctx->dctx.workspace = vzalloc(sz);
+	if (!zctx->dctx.workspace)
+		goto error;
+
+	ret = zlib_inflateInit2(&zctx->dctx, params->deflate.winbits);
+	if (ret != Z_OK)
+		goto error;
+
+	return 0;
+
+error:
+	deflate_destroy(ctx);
+	return -EINVAL;
+}
+
+static int deflate_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			    struct zcomp_req *req)
+{
+	struct deflate_ctx *zctx = ctx->context;
+	struct z_stream_s *deflate;
+	int ret;
+
+	deflate = &zctx->cctx;
+	ret = zlib_deflateReset(deflate);
+	if (ret != Z_OK)
+		return -EINVAL;
+
+	deflate->next_in = (u8 *)req->src;
+	deflate->avail_in = req->src_len;
+	deflate->next_out = (u8 *)req->dst;
+	deflate->avail_out = req->dst_len;
+
+	ret = zlib_deflate(deflate, Z_FINISH);
+	if (ret != Z_STREAM_END)
+		return -EINVAL;
+
+	req->dst_len = deflate->total_out;
+	return 0;
+}
+
+static int deflate_decompress(struct zcomp_params *params,
+			      struct zcomp_ctx *ctx,
+			      struct zcomp_req *req)
+{
+	struct deflate_ctx *zctx = ctx->context;
+	struct z_stream_s *inflate;
+	int ret;
+
+	inflate = &zctx->dctx;
+
+	ret = zlib_inflateReset(inflate);
+	if (ret != Z_OK)
+		return -EINVAL;
+
+	inflate->next_in = (u8 *)req->src;
+	inflate->avail_in = req->src_len;
+	inflate->next_out = (u8 *)req->dst;
+	inflate->avail_out = req->dst_len;
+
+	ret = zlib_inflate(inflate, Z_SYNC_FLUSH);
+	if (ret != Z_STREAM_END)
+		return -EINVAL;
+
+	return 0;
+}
+
+const struct zcomp_ops backend_deflate = {
+	.compress	= deflate_compress,
+	.decompress	= deflate_decompress,
+	.create_ctx	= deflate_create,
+	.destroy_ctx	= deflate_destroy,
+	.setup_params	= deflate_setup_params,
+	.release_params	= deflate_release_params,
+	.name		= "deflate",
+};
diff --git a/drivers/block/zram/backend_deflate.h b/drivers/block/zram/backend_deflate.h
new file mode 100644
index 000000000..a39ac12b1
--- /dev/null
+++ b/drivers/block/zram/backend_deflate.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_DEFLATE_H__
+#define __BACKEND_DEFLATE_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_deflate;
+
+#endif /* __BACKEND_DEFLATE_H__ */
diff --git a/drivers/block/zram/backend_lz4.c b/drivers/block/zram/backend_lz4.c
new file mode 100644
index 000000000..1e4ad31d3
--- /dev/null
+++ b/drivers/block/zram/backend_lz4.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "lz4: " fmt
+
+#include <linux/kernel.h>
+#include <linux/lz4.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#include "backend_lz4.h"
+
+struct lz4_ctx {
+	void *mem;
+
+	LZ4_streamDecode_t *dstrm;
+	LZ4_stream_t *cstrm;
+};
+
+static void lz4_release_params(struct zcomp_params *params)
+{
+	LZ4_stream_t *dict_stream = params->drv_data;
+
+	params->drv_data = NULL;
+	if (!dict_stream)
+		return;
+
+	kfree(dict_stream);
+}
+
+static int lz4_setup_params(struct zcomp_params *params)
+{
+	LZ4_stream_t *dict_stream;
+	int ret;
+
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
+		params->level = LZ4_ACCELERATION_DEFAULT;
+	} else if (params->level < LZ4_ACCELERATION_DEFAULT) {
+		pr_err("invalid compression level %d\n", params->level);
+		return -EINVAL;
+	}
+
+	if (!params->dict || !params->dict_sz)
+		return 0;
+
+	dict_stream = kzalloc_obj(*dict_stream);
+	if (!dict_stream)
+		return -ENOMEM;
+
+	ret = LZ4_loadDict(dict_stream,
+			   params->dict, params->dict_sz);
+	if (ret != params->dict_sz) {
+		kfree(dict_stream);
+		return -EINVAL;
+	}
+	params->drv_data = dict_stream;
+
+	return 0;
+}
+
+static void lz4_destroy(struct zcomp_ctx *ctx)
+{
+	struct lz4_ctx *zctx = ctx->context;
+
+	if (!zctx)
+		return;
+
+	vfree(zctx->mem);
+	kfree(zctx->dstrm);
+	kfree(zctx->cstrm);
+	kfree(zctx);
+}
+
+static int lz4_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	struct lz4_ctx *zctx;
+
+	zctx = kzalloc_obj(*zctx);
+	if (!zctx)
+		return -ENOMEM;
+
+	ctx->context = zctx;
+	if (params->dict_sz == 0) {
+		zctx->mem = vmalloc(LZ4_MEM_COMPRESS);
+		if (!zctx->mem)
+			goto error;
+	} else {
+		zctx->dstrm = kzalloc_obj(*zctx->dstrm);
+		if (!zctx->dstrm)
+			goto error;
+
+		zctx->cstrm = kzalloc_obj(*zctx->cstrm);
+		if (!zctx->cstrm)
+			goto error;
+	}
+
+	return 0;
+
+error:
+	lz4_destroy(ctx);
+	return -ENOMEM;
+}
+
+static int lz4_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			struct zcomp_req *req)
+{
+	struct lz4_ctx *zctx = ctx->context;
+	int ret;
+
+	if (!zctx->cstrm) {
+		ret = LZ4_compress_fast(req->src, req->dst, req->src_len,
+					req->dst_len, params->level,
+					zctx->mem);
+	} else {
+		/* Cstrm needs to be reset */
+		memcpy(zctx->cstrm, params->drv_data, sizeof(*zctx->cstrm));
+		ret = LZ4_compress_fast_continue(zctx->cstrm, req->src,
+						 req->dst, req->src_len,
+						 req->dst_len, params->level);
+	}
+	if (!ret)
+		return -EINVAL;
+	req->dst_len = ret;
+	return 0;
+}
+
+static int lz4_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			  struct zcomp_req *req)
+{
+	struct lz4_ctx *zctx = ctx->context;
+	int ret;
+
+	if (!zctx->dstrm) {
+		ret = LZ4_decompress_safe(req->src, req->dst, req->src_len,
+					  req->dst_len);
+	} else {
+		/* Dstrm needs to be reset */
+		ret = LZ4_setStreamDecode(zctx->dstrm, params->dict,
+					  params->dict_sz);
+		if (!ret)
+			return -EINVAL;
+		ret = LZ4_decompress_safe_continue(zctx->dstrm, req->src,
+						   req->dst, req->src_len,
+						   req->dst_len);
+	}
+	if (ret < 0)
+		return -EINVAL;
+	return 0;
+}
+
+const struct zcomp_ops backend_lz4 = {
+	.compress	= lz4_compress,
+	.decompress	= lz4_decompress,
+	.create_ctx	= lz4_create,
+	.destroy_ctx	= lz4_destroy,
+	.setup_params	= lz4_setup_params,
+	.release_params	= lz4_release_params,
+	.name		= "lz4",
+};
diff --git a/drivers/block/zram/backend_lz4.h b/drivers/block/zram/backend_lz4.h
new file mode 100644
index 000000000..c11fa602a
--- /dev/null
+++ b/drivers/block/zram/backend_lz4.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_LZ4_H__
+#define __BACKEND_LZ4_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_lz4;
+
+#endif /* __BACKEND_LZ4_H__ */
diff --git a/drivers/block/zram/backend_lz4hc.c b/drivers/block/zram/backend_lz4hc.c
new file mode 100644
index 000000000..d8aa01bb2
--- /dev/null
+++ b/drivers/block/zram/backend_lz4hc.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "lz4hc: " fmt
+
+#include <linux/kernel.h>
+#include <linux/lz4.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+
+#include "backend_lz4hc.h"
+
+struct lz4hc_ctx {
+	void *mem;
+
+	LZ4_streamDecode_t *dstrm;
+	LZ4_streamHC_t *cstrm;
+};
+
+static void lz4hc_release_params(struct zcomp_params *params)
+{
+}
+
+static int lz4hc_setup_params(struct zcomp_params *params)
+{
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
+		params->level = LZ4HC_DEFAULT_CLEVEL;
+	} else if (params->level < 1 || params->level > LZ4HC_MAX_CLEVEL) {
+		/*
+		 * Use < 1 rather than < LZ4HC_MIN_CLEVEL here because
+		 * LZ4HC_compress_generic() only clamps levels below 1
+		 * (levels 1 and 2 are valid). LZ4HC_MIN_CLEVEL (3) is
+		 * advisory and not enforced by the library.
+		 */
+		pr_err("invalid compression level %d\n", params->level);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static void lz4hc_destroy(struct zcomp_ctx *ctx)
+{
+	struct lz4hc_ctx *zctx = ctx->context;
+
+	if (!zctx)
+		return;
+
+	kfree(zctx->dstrm);
+	kfree(zctx->cstrm);
+	vfree(zctx->mem);
+	kfree(zctx);
+}
+
+static int lz4hc_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	struct lz4hc_ctx *zctx;
+
+	zctx = kzalloc_obj(*zctx);
+	if (!zctx)
+		return -ENOMEM;
+
+	ctx->context = zctx;
+	if (params->dict_sz == 0) {
+		zctx->mem = vmalloc(LZ4HC_MEM_COMPRESS);
+		if (!zctx->mem)
+			goto error;
+	} else {
+		zctx->dstrm = kzalloc_obj(*zctx->dstrm);
+		if (!zctx->dstrm)
+			goto error;
+
+		zctx->cstrm = kzalloc_obj(*zctx->cstrm);
+		if (!zctx->cstrm)
+			goto error;
+	}
+
+	return 0;
+
+error:
+	lz4hc_destroy(ctx);
+	return -EINVAL;
+}
+
+static int lz4hc_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			  struct zcomp_req *req)
+{
+	struct lz4hc_ctx *zctx = ctx->context;
+	int ret;
+
+	if (!zctx->cstrm) {
+		ret = LZ4_compress_HC(req->src, req->dst, req->src_len,
+				      req->dst_len, params->level,
+				      zctx->mem);
+	} else {
+		/* Cstrm needs to be reset */
+		LZ4_resetStreamHC(zctx->cstrm, params->level);
+		ret = LZ4_loadDictHC(zctx->cstrm, params->dict,
+				     params->dict_sz);
+		if (ret != params->dict_sz)
+			return -EINVAL;
+		ret = LZ4_compress_HC_continue(zctx->cstrm, req->src, req->dst,
+					       req->src_len, req->dst_len);
+	}
+	if (!ret)
+		return -EINVAL;
+	req->dst_len = ret;
+	return 0;
+}
+
+static int lz4hc_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			    struct zcomp_req *req)
+{
+	struct lz4hc_ctx *zctx = ctx->context;
+	int ret;
+
+	if (!zctx->dstrm) {
+		ret = LZ4_decompress_safe(req->src, req->dst, req->src_len,
+					  req->dst_len);
+	} else {
+		/* Dstrm needs to be reset */
+		ret = LZ4_setStreamDecode(zctx->dstrm, params->dict,
+					  params->dict_sz);
+		if (!ret)
+			return -EINVAL;
+		ret = LZ4_decompress_safe_continue(zctx->dstrm, req->src,
+						   req->dst, req->src_len,
+						   req->dst_len);
+	}
+	if (ret < 0)
+		return -EINVAL;
+	return 0;
+}
+
+const struct zcomp_ops backend_lz4hc = {
+	.compress	= lz4hc_compress,
+	.decompress	= lz4hc_decompress,
+	.create_ctx	= lz4hc_create,
+	.destroy_ctx	= lz4hc_destroy,
+	.setup_params	= lz4hc_setup_params,
+	.release_params	= lz4hc_release_params,
+	.name		= "lz4hc",
+};
diff --git a/drivers/block/zram/backend_lz4hc.h b/drivers/block/zram/backend_lz4hc.h
new file mode 100644
index 000000000..6de03551e
--- /dev/null
+++ b/drivers/block/zram/backend_lz4hc.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_LZ4HC_H__
+#define __BACKEND_LZ4HC_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_lz4hc;
+
+#endif /* __BACKEND_LZ4HC_H__ */
diff --git a/drivers/block/zram/backend_lzo.c b/drivers/block/zram/backend_lzo.c
new file mode 100644
index 000000000..d83f92cf7
--- /dev/null
+++ b/drivers/block/zram/backend_lzo.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "lzo: " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/lzo.h>
+
+#include "backend_lzo.h"
+
+static void lzo_release_params(struct zcomp_params *params)
+{
+}
+
+static int lzo_setup_params(struct zcomp_params *params)
+{
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	if (params->level != ZCOMP_PARAM_NOT_SET) {
+		pr_err("compression level is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+static int lzo_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	ctx->context = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
+	if (!ctx->context)
+		return -ENOMEM;
+	return 0;
+}
+
+static void lzo_destroy(struct zcomp_ctx *ctx)
+{
+	kfree(ctx->context);
+}
+
+static int lzo_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			struct zcomp_req *req)
+{
+	int ret;
+
+	ret = lzo1x_1_compress(req->src, req->src_len, req->dst,
+			       &req->dst_len, ctx->context);
+	return ret == LZO_E_OK ? 0 : ret;
+}
+
+static int lzo_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			  struct zcomp_req *req)
+{
+	int ret;
+
+	ret = lzo1x_decompress_safe(req->src, req->src_len,
+				    req->dst, &req->dst_len);
+	return ret == LZO_E_OK ? 0 : ret;
+}
+
+const struct zcomp_ops backend_lzo = {
+	.compress	= lzo_compress,
+	.decompress	= lzo_decompress,
+	.create_ctx	= lzo_create,
+	.destroy_ctx	= lzo_destroy,
+	.setup_params	= lzo_setup_params,
+	.release_params	= lzo_release_params,
+	.name		= "lzo",
+};
diff --git a/drivers/block/zram/backend_lzo.h b/drivers/block/zram/backend_lzo.h
new file mode 100644
index 000000000..93d54749e
--- /dev/null
+++ b/drivers/block/zram/backend_lzo.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_LZO_H__
+#define __BACKEND_LZO_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_lzo;
+
+#endif /* __BACKEND_LZO_H__ */
diff --git a/drivers/block/zram/backend_lzorle.c b/drivers/block/zram/backend_lzorle.c
new file mode 100644
index 000000000..1b120d062
--- /dev/null
+++ b/drivers/block/zram/backend_lzorle.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "lzo-rle: " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/lzo.h>
+
+#include "backend_lzorle.h"
+
+static void lzorle_release_params(struct zcomp_params *params)
+{
+}
+
+static int lzorle_setup_params(struct zcomp_params *params)
+{
+	if (params->dict_sz) {
+		pr_err("dictionary is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	if (params->level != ZCOMP_PARAM_NOT_SET) {
+		pr_err("compression level is not supported\n");
+		return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+static int lzorle_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	ctx->context = kzalloc(LZO1X_MEM_COMPRESS, GFP_KERNEL);
+	if (!ctx->context)
+		return -ENOMEM;
+	return 0;
+}
+
+static void lzorle_destroy(struct zcomp_ctx *ctx)
+{
+	kfree(ctx->context);
+}
+
+static int lzorle_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			   struct zcomp_req *req)
+{
+	int ret;
+
+	ret = lzorle1x_1_compress(req->src, req->src_len, req->dst,
+				  &req->dst_len, ctx->context);
+	return ret == LZO_E_OK ? 0 : ret;
+}
+
+static int lzorle_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			     struct zcomp_req *req)
+{
+	int ret;
+
+	ret = lzo1x_decompress_safe(req->src, req->src_len,
+				    req->dst, &req->dst_len);
+	return ret == LZO_E_OK ? 0 : ret;
+}
+
+const struct zcomp_ops backend_lzorle = {
+	.compress	= lzorle_compress,
+	.decompress	= lzorle_decompress,
+	.create_ctx	= lzorle_create,
+	.destroy_ctx	= lzorle_destroy,
+	.setup_params	= lzorle_setup_params,
+	.release_params	= lzorle_release_params,
+	.name		= "lzo-rle",
+};
diff --git a/drivers/block/zram/backend_lzorle.h b/drivers/block/zram/backend_lzorle.h
new file mode 100644
index 000000000..6ecb163b0
--- /dev/null
+++ b/drivers/block/zram/backend_lzorle.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_LZORLE_H__
+#define __BACKEND_LZORLE_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_lzorle;
+
+#endif /* __BACKEND_LZORLE_H__ */
diff --git a/drivers/block/zram/backend_zstd.c b/drivers/block/zram/backend_zstd.c
new file mode 100644
index 000000000..08da3810c
--- /dev/null
+++ b/drivers/block/zram/backend_zstd.c
@@ -0,0 +1,222 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#define pr_fmt(fmt) "zstd: " fmt
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/zstd.h>
+
+#include "backend_zstd.h"
+
+struct zstd_ctx {
+	zstd_cctx *cctx;
+	zstd_dctx *dctx;
+	void *cctx_mem;
+	void *dctx_mem;
+};
+
+struct zstd_params {
+	zstd_custom_mem custom_mem;
+	zstd_cdict *cdict;
+	zstd_ddict *ddict;
+	zstd_parameters cprm;
+};
+
+/*
+ * For C/D dictionaries we need to provide zstd with zstd_custom_mem,
+ * which zstd uses internally to allocate/free memory when needed.
+ */
+static void *zstd_custom_alloc(void *opaque, size_t size)
+{
+	return kvzalloc(size, GFP_NOIO | __GFP_NOWARN);
+}
+
+static void zstd_custom_free(void *opaque, void *address)
+{
+	kvfree(address);
+}
+
+static void zstd_release_params(struct zcomp_params *params)
+{
+	struct zstd_params *zp = params->drv_data;
+
+	params->drv_data = NULL;
+	if (!zp)
+		return;
+
+	zstd_free_cdict(zp->cdict);
+	zstd_free_ddict(zp->ddict);
+	kfree(zp);
+}
+
+static int zstd_setup_params(struct zcomp_params *params)
+{
+	zstd_compression_parameters prm;
+	struct zstd_params *zp;
+
+	zp = kzalloc_obj(*zp);
+	if (!zp)
+		return -ENOMEM;
+
+	params->drv_data = zp;
+	if (params->level == ZCOMP_PARAM_NOT_SET) {
+		params->level = zstd_default_clevel();
+	} else if (params->level < zstd_min_clevel() ||
+		   params->level > zstd_max_clevel()) {
+		pr_err("invalid compression level %d\n", params->level);
+		goto error;
+	}
+
+	zp->cprm = zstd_get_params(params->level, PAGE_SIZE);
+
+	zp->custom_mem.customAlloc = zstd_custom_alloc;
+	zp->custom_mem.customFree = zstd_custom_free;
+
+	prm = zstd_get_cparams(params->level, PAGE_SIZE,
+			       params->dict_sz);
+
+	zp->cdict = zstd_create_cdict_byreference(params->dict,
+						  params->dict_sz,
+						  prm,
+						  zp->custom_mem);
+	if (!zp->cdict)
+		goto error;
+
+	zp->ddict = zstd_create_ddict_byreference(params->dict,
+						  params->dict_sz,
+						  zp->custom_mem);
+	if (!zp->ddict)
+		goto error;
+
+	return 0;
+
+error:
+	return -EINVAL;
+}
+
+static void zstd_destroy(struct zcomp_ctx *ctx)
+{
+	struct zstd_ctx *zctx = ctx->context;
+
+	if (!zctx)
+		return;
+
+	/*
+	 * If ->cctx_mem and ->dctx_mem were allocated then we didn't use
+	 * C/D dictionary and ->cctx / ->dctx were "embedded" into these
+	 * buffers.
+	 *
+	 * If otherwise then we need to explicitly release ->cctx / ->dctx.
+	 */
+	if (zctx->cctx_mem)
+		vfree(zctx->cctx_mem);
+	else
+		zstd_free_cctx(zctx->cctx);
+
+	if (zctx->dctx_mem)
+		vfree(zctx->dctx_mem);
+	else
+		zstd_free_dctx(zctx->dctx);
+
+	kfree(zctx);
+}
+
+static int zstd_create(struct zcomp_params *params, struct zcomp_ctx *ctx)
+{
+	struct zstd_ctx *zctx;
+	zstd_parameters prm;
+	size_t sz;
+
+	zctx = kzalloc_obj(*zctx);
+	if (!zctx)
+		return -ENOMEM;
+
+	ctx->context = zctx;
+	if (params->dict_sz == 0) {
+		prm = zstd_get_params(params->level, PAGE_SIZE);
+		sz = zstd_cctx_workspace_bound(&prm.cParams);
+		zctx->cctx_mem = vzalloc(sz);
+		if (!zctx->cctx_mem)
+			goto error;
+
+		zctx->cctx = zstd_init_cctx(zctx->cctx_mem, sz);
+		if (!zctx->cctx)
+			goto error;
+
+		sz = zstd_dctx_workspace_bound();
+		zctx->dctx_mem = vzalloc(sz);
+		if (!zctx->dctx_mem)
+			goto error;
+
+		zctx->dctx = zstd_init_dctx(zctx->dctx_mem, sz);
+		if (!zctx->dctx)
+			goto error;
+	} else {
+		struct zstd_params *zp = params->drv_data;
+
+		zctx->cctx = zstd_create_cctx_advanced(zp->custom_mem);
+		if (!zctx->cctx)
+			goto error;
+
+		zctx->dctx = zstd_create_dctx_advanced(zp->custom_mem);
+		if (!zctx->dctx)
+			goto error;
+	}
+
+	return 0;
+
+error:
+	zstd_destroy(ctx);
+	return -EINVAL;
+}
+
+static int zstd_compress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			 struct zcomp_req *req)
+{
+	struct zstd_params *zp = params->drv_data;
+	struct zstd_ctx *zctx = ctx->context;
+	size_t ret;
+
+	if (params->dict_sz == 0)
+		ret = zstd_compress_cctx(zctx->cctx, req->dst, req->dst_len,
+					 req->src, req->src_len, &zp->cprm);
+	else
+		ret = zstd_compress_using_cdict(zctx->cctx, req->dst,
+						req->dst_len, req->src,
+						req->src_len,
+						zp->cdict);
+	if (zstd_is_error(ret))
+		return -EINVAL;
+	req->dst_len = ret;
+	return 0;
+}
+
+static int zstd_decompress(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			   struct zcomp_req *req)
+{
+	struct zstd_params *zp = params->drv_data;
+	struct zstd_ctx *zctx = ctx->context;
+	size_t ret;
+
+	if (params->dict_sz == 0)
+		ret = zstd_decompress_dctx(zctx->dctx, req->dst, req->dst_len,
+					   req->src, req->src_len);
+	else
+		ret = zstd_decompress_using_ddict(zctx->dctx, req->dst,
+						  req->dst_len, req->src,
+						  req->src_len, zp->ddict);
+	if (zstd_is_error(ret))
+		return -EINVAL;
+	return 0;
+}
+
+const struct zcomp_ops backend_zstd = {
+	.compress	= zstd_compress,
+	.decompress	= zstd_decompress,
+	.create_ctx	= zstd_create,
+	.destroy_ctx	= zstd_destroy,
+	.setup_params	= zstd_setup_params,
+	.release_params	= zstd_release_params,
+	.name		= "zstd",
+};
diff --git a/drivers/block/zram/backend_zstd.h b/drivers/block/zram/backend_zstd.h
new file mode 100644
index 000000000..10fdfff1e
--- /dev/null
+++ b/drivers/block/zram/backend_zstd.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#ifndef __BACKEND_ZSTD_H__
+#define __BACKEND_ZSTD_H__
+
+#include "zcomp.h"
+
+extern const struct zcomp_ops backend_zstd;
+
+#endif /* __BACKEND_ZSTD_H__ */
diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
new file mode 100644
index 000000000..974c46918
--- /dev/null
+++ b/drivers/block/zram/zcomp.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+#include <linux/cpuhotplug.h>
+#include <linux/vmalloc.h>
+#include <linux/sysfs.h>
+
+#include "zcomp.h"
+
+#include "backend_lzo.h"
+#include "backend_lzorle.h"
+#include "backend_lz4.h"
+#include "backend_lz4hc.h"
+#include "backend_zstd.h"
+#include "backend_deflate.h"
+#include "backend_842.h"
+
+static const struct zcomp_ops *backends[] = {
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZO)
+	&backend_lzorle,
+	&backend_lzo,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZ4)
+	&backend_lz4,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_LZ4HC)
+	&backend_lz4hc,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_ZSTD)
+	&backend_zstd,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_DEFLATE)
+	&backend_deflate,
+#endif
+#if IS_ENABLED(CONFIG_ZRAM_BACKEND_842)
+	&backend_842,
+#endif
+	NULL
+};
+
+static void zcomp_strm_free(struct zcomp *comp, struct zcomp_strm *zstrm)
+{
+	comp->ops->destroy_ctx(&zstrm->ctx);
+	vfree(zstrm->local_copy);
+	vfree(zstrm->buffer);
+	zstrm->buffer = NULL;
+}
+
+static int zcomp_strm_init(struct zcomp *comp, struct zcomp_strm *zstrm)
+{
+	int ret;
+
+	ret = comp->ops->create_ctx(comp->params, &zstrm->ctx);
+	if (ret)
+		return ret;
+
+	zstrm->local_copy = vzalloc(PAGE_SIZE);
+	/*
+	 * allocate 2 pages. 1 for compressed data, plus 1 extra for the
+	 * case when compressed size is larger than the original one
+	 */
+	zstrm->buffer = vzalloc(2 * PAGE_SIZE);
+	if (!zstrm->buffer || !zstrm->local_copy) {
+		zcomp_strm_free(comp, zstrm);
+		return -ENOMEM;
+	}
+	return 0;
+}
+
+static const struct zcomp_ops *lookup_backend_ops(const char *comp)
+{
+	int i = 0;
+
+	while (backends[i]) {
+		if (sysfs_streq(comp, backends[i]->name))
+			break;
+		i++;
+	}
+	return backends[i];
+}
+
+const char *zcomp_lookup_backend_name(const char *comp)
+{
+	const struct zcomp_ops *backend = lookup_backend_ops(comp);
+
+	if (backend)
+		return backend->name;
+
+	return NULL;
+}
+
+/* show available compressors */
+ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(backends) - 1; i++) {
+		if (!strcmp(comp, backends[i]->name)) {
+			at += sysfs_emit_at(buf, at, "[%s] ",
+					    backends[i]->name);
+		} else {
+			at += sysfs_emit_at(buf, at, "%s ", backends[i]->name);
+		}
+	}
+
+	at += sysfs_emit_at(buf, at, "\n");
+	return at;
+}
+
+struct zcomp_strm *zcomp_stream_get(struct zcomp *comp)
+{
+	for (;;) {
+		struct zcomp_strm *zstrm = raw_cpu_ptr(comp->stream);
+
+		/*
+		 * Inspired by zswap
+		 *
+		 * stream is returned with ->mutex locked which prevents
+		 * cpu_dead() from releasing this stream under us, however
+		 * there is still a race window between raw_cpu_ptr() and
+		 * mutex_lock(), during which we could have been migrated
+		 * from a CPU that has already destroyed its stream.  If
+		 * so then unlock and re-try on the current CPU.
+		 */
+		mutex_lock(&zstrm->lock);
+		if (likely(zstrm->buffer))
+			return zstrm;
+		mutex_unlock(&zstrm->lock);
+	}
+}
+
+void zcomp_stream_put(struct zcomp_strm *zstrm)
+{
+	mutex_unlock(&zstrm->lock);
+}
+
+int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		   const void *src, unsigned int *dst_len)
+{
+	struct zcomp_req req = {
+		.src = src,
+		.dst = zstrm->buffer,
+		.src_len = PAGE_SIZE,
+		.dst_len = 2 * PAGE_SIZE,
+	};
+	int ret;
+
+	might_sleep();
+	ret = comp->ops->compress(comp->params, &zstrm->ctx, &req);
+	if (!ret)
+		*dst_len = req.dst_len;
+	return ret;
+}
+
+int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		     const void *src, unsigned int src_len, void *dst)
+{
+	struct zcomp_req req = {
+		.src = src,
+		.dst = dst,
+		.src_len = src_len,
+		.dst_len = PAGE_SIZE,
+	};
+
+	might_sleep();
+	return comp->ops->decompress(comp->params, &zstrm->ctx, &req);
+}
+
+int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node)
+{
+	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
+	struct zcomp_strm *zstrm = per_cpu_ptr(comp->stream, cpu);
+	int ret;
+
+	ret = zcomp_strm_init(comp, zstrm);
+	if (ret)
+		pr_err("Can't allocate a compression stream\n");
+	return ret;
+}
+
+int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node)
+{
+	struct zcomp *comp = hlist_entry(node, struct zcomp, node);
+	struct zcomp_strm *zstrm = per_cpu_ptr(comp->stream, cpu);
+
+	mutex_lock(&zstrm->lock);
+	zcomp_strm_free(comp, zstrm);
+	mutex_unlock(&zstrm->lock);
+	return 0;
+}
+
+static int zcomp_init(struct zcomp *comp, struct zcomp_params *params)
+{
+	int ret, cpu;
+
+	comp->stream = alloc_percpu(struct zcomp_strm);
+	if (!comp->stream)
+		return -ENOMEM;
+
+	comp->params = params;
+	ret = comp->ops->setup_params(comp->params);
+	if (ret)
+		goto cleanup;
+
+	for_each_possible_cpu(cpu)
+		mutex_init(&per_cpu_ptr(comp->stream, cpu)->lock);
+
+	ret = cpuhp_state_add_instance(CPUHP_ZCOMP_PREPARE, &comp->node);
+	if (ret < 0)
+		goto cleanup;
+
+	return 0;
+
+cleanup:
+	comp->ops->release_params(comp->params);
+	free_percpu(comp->stream);
+	return ret;
+}
+
+void zcomp_destroy(struct zcomp *comp)
+{
+	cpuhp_state_remove_instance(CPUHP_ZCOMP_PREPARE, &comp->node);
+	comp->ops->release_params(comp->params);
+	free_percpu(comp->stream);
+	kfree(comp);
+}
+
+struct zcomp *zcomp_create(const char *alg, struct zcomp_params *params)
+{
+	struct zcomp *comp;
+	int error;
+
+	/*
+	 * The backends array has a sentinel NULL value, so the minimum
+	 * size is 1. In order to be valid the array, apart from the
+	 * sentinel NULL element, should have at least one compression
+	 * backend selected.
+	 */
+	BUILD_BUG_ON(ARRAY_SIZE(backends) <= 1);
+
+	comp = kzalloc_obj(struct zcomp);
+	if (!comp)
+		return ERR_PTR(-ENOMEM);
+
+	comp->ops = lookup_backend_ops(alg);
+	if (!comp->ops) {
+		kfree(comp);
+		return ERR_PTR(-EINVAL);
+	}
+
+	error = zcomp_init(comp, params);
+	if (error) {
+		kfree(comp);
+		return ERR_PTR(error);
+	}
+	return comp;
+}
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
new file mode 100644
index 000000000..81a0f3f6f
--- /dev/null
+++ b/drivers/block/zram/zcomp.h
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _ZCOMP_H_
+#define _ZCOMP_H_
+
+#include <linux/mutex.h>
+
+#define ZCOMP_PARAM_NOT_SET	INT_MIN
+
+struct deflate_params {
+	s32 winbits;
+};
+
+/*
+ * Immutable driver (backend) parameters. The driver may attach private
+ * data to it (e.g. driver representation of the dictionary, etc.).
+ *
+ * This data is kept per-comp and is shared among execution contexts.
+ */
+struct zcomp_params {
+	void *dict;
+	size_t dict_sz;
+	s32 level;
+	union {
+		struct deflate_params deflate;
+	};
+
+	void *drv_data;
+};
+
+/*
+ * Run-time driver context - scratch buffers, etc. It is modified during
+ * request execution (compression/decompression), cannot be shared, so
+ * it's in per-CPU area.
+ */
+struct zcomp_ctx {
+	void *context;
+};
+
+struct zcomp_strm {
+	struct mutex lock;
+	/* compression buffer */
+	void *buffer;
+	/* local copy of handle memory */
+	void *local_copy;
+	struct zcomp_ctx ctx;
+};
+
+struct zcomp_req {
+	const unsigned char *src;
+	const size_t src_len;
+
+	unsigned char *dst;
+	size_t dst_len;
+};
+
+struct zcomp_ops {
+	int (*compress)(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			struct zcomp_req *req);
+	int (*decompress)(struct zcomp_params *params, struct zcomp_ctx *ctx,
+			  struct zcomp_req *req);
+
+	int (*create_ctx)(struct zcomp_params *params, struct zcomp_ctx *ctx);
+	void (*destroy_ctx)(struct zcomp_ctx *ctx);
+
+	int (*setup_params)(struct zcomp_params *params);
+	void (*release_params)(struct zcomp_params *params);
+
+	const char *name;
+};
+
+/* dynamic per-device compression frontend */
+struct zcomp {
+	struct zcomp_strm __percpu *stream;
+	const struct zcomp_ops *ops;
+	struct zcomp_params *params;
+	struct hlist_node node;
+};
+
+int zcomp_cpu_up_prepare(unsigned int cpu, struct hlist_node *node);
+int zcomp_cpu_dead(unsigned int cpu, struct hlist_node *node);
+ssize_t zcomp_available_show(const char *comp, char *buf, ssize_t at);
+const char *zcomp_lookup_backend_name(const char *comp);
+
+struct zcomp *zcomp_create(const char *alg, struct zcomp_params *params);
+void zcomp_destroy(struct zcomp *comp);
+
+struct zcomp_strm *zcomp_stream_get(struct zcomp *comp);
+void zcomp_stream_put(struct zcomp_strm *zstrm);
+
+int zcomp_compress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		   const void *src, unsigned int *dst_len);
+int zcomp_decompress(struct zcomp *comp, struct zcomp_strm *zstrm,
+		     const void *src, unsigned int src_len, void *dst);
+
+#endif /* _ZCOMP_H_ */
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
new file mode 100644
index 000000000..a9b3bb1d3
--- /dev/null
+++ b/drivers/block/zram/zram_drv.c
@@ -0,0 +1,3323 @@
+/*
+ * Compressed RAM block device
+ *
+ * Copyright (C) 2008, 2009, 2010  Nitin Gupta
+ *               2012, 2013 Minchan Kim
+ *
+ * This code is released using a dual license strategy: BSD/GPL
+ * You can choose the licence that better fits your requirements.
+ *
+ * Released under the terms of 3-clause BSD License
+ * Released under the terms of GNU General Public License Version 2.0
+ *
+ */
+
+#define pr_fmt(fmt) "zram: " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/bio.h>
+#include <linux/bitops.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>
+#include <linux/device.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+#include <linux/backing-dev.h>
+#include <linux/string.h>
+#include <linux/vmalloc.h>
+#include <linux/err.h>
+#include <linux/idr.h>
+#include <linux/sysfs.h>
+#include <linux/debugfs.h>
+#include <linux/cpuhotplug.h>
+#include <linux/part_stat.h>
+#include <linux/kernel_read_file.h>
+#include <linux/rcupdate.h>
+
+#include "zram_drv.h"
+
+static DEFINE_IDR(zram_index_idr);
+/* idr index must be protected */
+static DEFINE_MUTEX(zram_index_mutex);
+
+static int zram_major;
+static const char *default_compressor = CONFIG_ZRAM_DEF_COMP;
+
+#define ZRAM_MAX_ALGO_NAME_SZ	128
+
+/* Module params (documentation at end) */
+static unsigned int num_devices = 1;
+/*
+ * Pages that compress to sizes equals or greater than this are stored
+ * uncompressed in memory.
+ */
+static size_t huge_class_size;
+
+static const struct block_device_operations zram_devops;
+
+static void slot_free(struct zram *zram, unsigned long index);
+
+/*
+ * entry locking rules:
+ *
+ * 1) Lock is exclusive
+ *
+ * 2) lock() function can sleep waiting for the lock
+ *
+ * 3) Lock owner can sleep
+ *
+ * 4) Use TRY lock variant when in atomic context
+ *    - must check return value and handle locking failers
+ */
+static __must_check bool slot_trylock(struct zram *zram, unsigned long index)
+{
+	unsigned long *lock = &zram->table[index].__lock;
+
+	if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK_BIT, lock)) {
+		mutex_acquire(&zram->table_lock_map, 0, 1, _RET_IP_);
+		lock_acquired(&zram->table_lock_map, _RET_IP_);
+		return true;
+	}
+
+	return false;
+}
+
+static void slot_lock(struct zram *zram, unsigned long index)
+{
+	unsigned long *lock = &zram->table[index].__lock;
+
+	mutex_acquire(&zram->table_lock_map, 0, 0, _RET_IP_);
+	wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK_BIT, TASK_UNINTERRUPTIBLE);
+	lock_acquired(&zram->table_lock_map, _RET_IP_);
+}
+
+static void slot_unlock(struct zram *zram, unsigned long index)
+{
+	unsigned long *lock = &zram->table[index].__lock;
+
+	mutex_release(&zram->table_lock_map, _RET_IP_);
+	clear_and_wake_up_bit(ZRAM_ENTRY_LOCK_BIT, lock);
+}
+
+static inline bool init_done(struct zram *zram)
+{
+	return zram->disksize;
+}
+
+static inline struct zram *dev_to_zram(struct device *dev)
+{
+	return (struct zram *)dev_to_disk(dev)->private_data;
+}
+
+static unsigned long get_slot_handle(struct zram *zram, unsigned long index)
+{
+	return zram->table[index].handle;
+}
+
+static void set_slot_handle(struct zram *zram, unsigned long index,
+			    unsigned long handle)
+{
+	zram->table[index].handle = handle;
+}
+
+static bool test_slot_flag(struct zram *zram, unsigned long index,
+			   enum zram_pageflags flag)
+{
+	return zram->table[index].attr.flags & BIT(flag);
+}
+
+static void set_slot_flag(struct zram *zram, unsigned long index,
+			  enum zram_pageflags flag)
+{
+	zram->table[index].attr.flags |= BIT(flag);
+}
+
+static void clear_slot_flag(struct zram *zram, unsigned long index,
+			    enum zram_pageflags flag)
+{
+	zram->table[index].attr.flags &= ~BIT(flag);
+}
+
+static size_t get_slot_size(struct zram *zram, unsigned long index)
+{
+	return zram->table[index].attr.flags & (BIT(ZRAM_FLAG_SHIFT) - 1);
+}
+
+static void set_slot_size(struct zram *zram, unsigned long index, size_t size)
+{
+	unsigned long flags = zram->table[index].attr.flags >> ZRAM_FLAG_SHIFT;
+
+	zram->table[index].attr.flags = (flags << ZRAM_FLAG_SHIFT) | size;
+}
+
+static inline bool slot_allocated(struct zram *zram, unsigned long index)
+{
+	return get_slot_size(zram, index) ||
+		test_slot_flag(zram, index, ZRAM_SAME) ||
+		test_slot_flag(zram, index, ZRAM_WB);
+}
+
+static inline void set_slot_comp_priority(struct zram *zram,
+					  unsigned long index, u32 prio)
+{
+	prio &= ZRAM_COMP_PRIORITY_MASK;
+	/*
+	 * Clear previous priority value first, in case if we recompress
+	 * further an already recompressed page
+	 */
+	zram->table[index].attr.flags &= ~(ZRAM_COMP_PRIORITY_MASK <<
+					   ZRAM_COMP_PRIORITY_BIT1);
+	zram->table[index].attr.flags |= (prio << ZRAM_COMP_PRIORITY_BIT1);
+}
+
+static inline u32 get_slot_comp_priority(struct zram *zram, unsigned long index)
+{
+	u32 prio = zram->table[index].attr.flags >> ZRAM_COMP_PRIORITY_BIT1;
+
+	return prio & ZRAM_COMP_PRIORITY_MASK;
+}
+
+static void mark_slot_accessed(struct zram *zram, unsigned long index)
+{
+	clear_slot_flag(zram, index, ZRAM_IDLE);
+	clear_slot_flag(zram, index, ZRAM_PP_SLOT);
+#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
+	zram->table[index].attr.ac_time = (u32)ktime_get_boottime_seconds();
+#endif
+}
+
+static inline void update_used_max(struct zram *zram, const unsigned long pages)
+{
+	unsigned long cur_max = atomic_long_read(&zram->stats.max_used_pages);
+
+	do {
+		if (cur_max >= pages)
+			return;
+	} while (!atomic_long_try_cmpxchg(&zram->stats.max_used_pages,
+					  &cur_max, pages));
+}
+
+static bool zram_can_store_page(struct zram *zram)
+{
+	unsigned long alloced_pages;
+
+	alloced_pages = zs_get_total_pages(zram->mem_pool);
+	update_used_max(zram, alloced_pages);
+
+	return !zram->limit_pages || alloced_pages <= zram->limit_pages;
+}
+
+#if PAGE_SIZE != 4096
+static inline bool is_partial_io(struct bio_vec *bvec)
+{
+	return bvec->bv_len != PAGE_SIZE;
+}
+#define ZRAM_PARTIAL_IO		1
+#else
+static inline bool is_partial_io(struct bio_vec *bvec)
+{
+	return false;
+}
+#endif
+
+#if defined CONFIG_ZRAM_WRITEBACK || defined CONFIG_ZRAM_MULTI_COMP
+struct zram_pp_slot {
+	unsigned long		index;
+	struct list_head	entry;
+};
+
+/*
+ * A post-processing bucket is, essentially, a size class, this defines
+ * the range (in bytes) of pp-slots sizes in particular bucket.
+ */
+#define PP_BUCKET_SIZE_RANGE	64
+#define NUM_PP_BUCKETS		((PAGE_SIZE / PP_BUCKET_SIZE_RANGE) + 1)
+
+struct zram_pp_ctl {
+	struct list_head	pp_buckets[NUM_PP_BUCKETS];
+};
+
+static struct zram_pp_ctl *init_pp_ctl(void)
+{
+	struct zram_pp_ctl *ctl;
+	u32 idx;
+
+	ctl = kmalloc_obj(*ctl);
+	if (!ctl)
+		return NULL;
+
+	for (idx = 0; idx < NUM_PP_BUCKETS; idx++)
+		INIT_LIST_HEAD(&ctl->pp_buckets[idx]);
+	return ctl;
+}
+
+static void release_pp_slot(struct zram *zram, struct zram_pp_slot *pps)
+{
+	list_del_init(&pps->entry);
+
+	slot_lock(zram, pps->index);
+	clear_slot_flag(zram, pps->index, ZRAM_PP_SLOT);
+	slot_unlock(zram, pps->index);
+
+	kfree(pps);
+}
+
+static void release_pp_ctl(struct zram *zram, struct zram_pp_ctl *ctl)
+{
+	u32 idx;
+
+	if (!ctl)
+		return;
+
+	for (idx = 0; idx < NUM_PP_BUCKETS; idx++) {
+		while (!list_empty(&ctl->pp_buckets[idx])) {
+			struct zram_pp_slot *pps;
+
+			pps = list_first_entry(&ctl->pp_buckets[idx],
+					       struct zram_pp_slot,
+					       entry);
+			release_pp_slot(zram, pps);
+		}
+	}
+
+	kfree(ctl);
+}
+
+static bool place_pp_slot(struct zram *zram, struct zram_pp_ctl *ctl,
+			  unsigned long index)
+{
+	struct zram_pp_slot *pps;
+	u32 bid;
+
+	pps = kmalloc_obj(*pps, GFP_NOIO | __GFP_NOWARN);
+	if (!pps)
+		return false;
+
+	INIT_LIST_HEAD(&pps->entry);
+	pps->index = index;
+
+	bid = get_slot_size(zram, pps->index) / PP_BUCKET_SIZE_RANGE;
+	list_add(&pps->entry, &ctl->pp_buckets[bid]);
+
+	set_slot_flag(zram, pps->index, ZRAM_PP_SLOT);
+	return true;
+}
+
+static struct zram_pp_slot *select_pp_slot(struct zram_pp_ctl *ctl)
+{
+	struct zram_pp_slot *pps = NULL;
+	s32 idx = NUM_PP_BUCKETS - 1;
+
+	/* The higher the bucket id the more optimal slot post-processing is */
+	while (idx >= 0) {
+		pps = list_first_entry_or_null(&ctl->pp_buckets[idx],
+					       struct zram_pp_slot,
+					       entry);
+		if (pps)
+			break;
+
+		idx--;
+	}
+	return pps;
+}
+#endif
+
+static inline void zram_fill_page(void *ptr, unsigned long len,
+					unsigned long value)
+{
+	WARN_ON_ONCE(!IS_ALIGNED(len, sizeof(unsigned long)));
+	memset_l(ptr, value, len / sizeof(unsigned long));
+}
+
+static bool page_same_filled(void *ptr, unsigned long *element)
+{
+	unsigned long *page;
+	unsigned long val;
+	unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;
+
+	page = (unsigned long *)ptr;
+	val = page[0];
+
+	if (val != page[last_pos])
+		return false;
+
+	for (pos = 1; pos < last_pos; pos++) {
+		if (val != page[pos])
+			return false;
+	}
+
+	*element = val;
+
+	return true;
+}
+
+static ssize_t initstate_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	u32 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	guard(rwsem_read)(&zram->dev_lock);
+	val = init_done(zram);
+
+	return sysfs_emit(buf, "%u\n", val);
+}
+
+static ssize_t disksize_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return sysfs_emit(buf, "%llu\n", zram->disksize);
+}
+
+static ssize_t mem_limit_store(struct device *dev,
+			       struct device_attribute *attr, const char *buf,
+			       size_t len)
+{
+	u64 limit;
+	char *tmp;
+	struct zram *zram = dev_to_zram(dev);
+
+	limit = memparse(buf, &tmp);
+	if (buf == tmp) /* no chars parsed, invalid input */
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	zram->limit_pages = PAGE_ALIGN(limit) >> PAGE_SHIFT;
+
+	return len;
+}
+
+static ssize_t mem_used_max_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	int err;
+	unsigned long val;
+	struct zram *zram = dev_to_zram(dev);
+
+	err = kstrtoul(buf, 10, &val);
+	if (err || val != 0)
+		return -EINVAL;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	if (init_done(zram)) {
+		atomic_long_set(&zram->stats.max_used_pages,
+				zs_get_total_pages(zram->mem_pool));
+	}
+
+	return len;
+}
+
+/*
+ * Mark all pages which are older than or equal to cutoff as IDLE.
+ * Callers should hold the zram init lock in read mode
+ */
+static void mark_idle(struct zram *zram, ktime_t cutoff)
+{
+	int is_idle = 1;
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	unsigned long index;
+
+	for (index = 0; index < nr_pages; index++) {
+		/*
+		 * Do not mark ZRAM_SAME slots as ZRAM_IDLE, because no
+		 * post-processing (recompress, writeback) happens to the
+		 * ZRAM_SAME slot.
+		 *
+		 * And ZRAM_WB slots simply cannot be ZRAM_IDLE.
+		 */
+		slot_lock(zram, index);
+		if (!slot_allocated(zram, index) ||
+		    test_slot_flag(zram, index, ZRAM_WB) ||
+		    test_slot_flag(zram, index, ZRAM_SAME)) {
+			slot_unlock(zram, index);
+			continue;
+		}
+
+#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
+		is_idle = !cutoff ||
+			ktime_after(cutoff, zram->table[index].attr.ac_time);
+#endif
+		if (is_idle)
+			set_slot_flag(zram, index, ZRAM_IDLE);
+		else
+			clear_slot_flag(zram, index, ZRAM_IDLE);
+		slot_unlock(zram, index);
+	}
+}
+
+static ssize_t idle_store(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ktime_t cutoff = 0;
+
+	if (!sysfs_streq(buf, "all")) {
+		/*
+		 * If it did not parse as 'all' try to treat it as an integer
+		 * when we have memory tracking enabled.
+		 */
+		u32 age_sec;
+
+		if (IS_ENABLED(CONFIG_ZRAM_TRACK_ENTRY_ACTIME) &&
+		    !kstrtouint(buf, 0, &age_sec))
+			cutoff = ktime_sub((u32)ktime_get_boottime_seconds(),
+					   age_sec);
+		else
+			return -EINVAL;
+	}
+
+	guard(rwsem_read)(&zram->dev_lock);
+	if (!init_done(zram))
+		return -EINVAL;
+
+	/*
+	 * A cutoff of 0 marks everything as idle, this is the
+	 * "all" behavior.
+	 */
+	mark_idle(zram, cutoff);
+	return len;
+}
+
+#ifdef CONFIG_ZRAM_WRITEBACK
+#define INVALID_BDEV_BLOCK		(~0UL)
+
+static int read_from_zspool_raw(struct zram *zram, struct page *page,
+				unsigned long index);
+static int read_from_zspool(struct zram *zram, struct page *page,
+			    unsigned long index);
+
+struct zram_wb_ctl {
+	/* idle list is accessed only by the writeback task, no concurency */
+	struct list_head idle_reqs;
+	/* done list is accessed concurrently, protect by done_lock */
+	struct list_head done_reqs;
+	wait_queue_head_t done_wait;
+	spinlock_t done_lock;
+	atomic_t num_inflight;
+	struct rcu_head rcu;
+};
+
+struct zram_wb_req {
+	unsigned long blk_idx;
+	struct page *page;
+	struct zram_pp_slot *pps;
+	struct bio_vec bio_vec;
+	struct bio bio;
+
+	struct list_head entry;
+};
+
+struct zram_rb_req {
+	struct work_struct work;
+	struct zram *zram;
+	struct page *page;
+	/* The read bio for backing device */
+	struct bio *bio;
+	unsigned long blk_idx;
+	union {
+		/* The original bio to complete (async read) */
+		struct bio *parent;
+		/* error status (sync read) */
+		int error;
+	};
+	unsigned long index;
+};
+
+#define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
+static ssize_t bd_stat_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	ret = sysfs_emit(buf,
+			 "%8llu %8llu %8llu\n",
+			 FOUR_K((u64)atomic64_read(&zram->stats.bd_count)),
+			 FOUR_K((u64)atomic64_read(&zram->stats.bd_reads)),
+			 FOUR_K((u64)atomic64_read(&zram->stats.bd_writes)));
+
+	return ret;
+}
+
+static ssize_t compressed_writeback_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	bool val;
+
+	if (kstrtobool(buf, &val))
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram)) {
+		return -EBUSY;
+	}
+
+	zram->compressed_wb = val;
+
+	return len;
+}
+
+static ssize_t compressed_writeback_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	bool val;
+	struct zram *zram = dev_to_zram(dev);
+
+	guard(rwsem_read)(&zram->dev_lock);
+	val = zram->compressed_wb;
+
+	return sysfs_emit(buf, "%d\n", val);
+}
+
+static ssize_t writeback_limit_enable_store(struct device *dev,
+					    struct device_attribute *attr,
+					    const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u64 val;
+
+	if (kstrtoull(buf, 10, &val))
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	zram->wb_limit_enable = val;
+
+	return len;
+}
+
+static ssize_t writeback_limit_enable_show(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	bool val;
+	struct zram *zram = dev_to_zram(dev);
+
+	guard(rwsem_read)(&zram->dev_lock);
+	val = zram->wb_limit_enable;
+
+	return sysfs_emit(buf, "%d\n", val);
+}
+
+static ssize_t writeback_limit_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u64 val;
+
+	if (kstrtoull(buf, 10, &val))
+		return -EINVAL;
+
+	/*
+	 * When the page size is greater than 4KB, if bd_wb_limit is set to
+	 * a value that is not page - size aligned, it will cause value
+	 * wrapping. For example, when the page size is set to 16KB and
+	 * bd_wb_limit is set to 3, a single write - back operation will
+	 * cause bd_wb_limit to become -1. Even more terrifying is that
+	 * bd_wb_limit is an unsigned number.
+	 */
+	val = rounddown(val, PAGE_SIZE / 4096);
+
+	guard(rwsem_write)(&zram->dev_lock);
+	zram->bd_wb_limit = val;
+
+	return len;
+}
+
+static ssize_t writeback_limit_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	u64 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	guard(rwsem_read)(&zram->dev_lock);
+	val = zram->bd_wb_limit;
+
+	return sysfs_emit(buf, "%llu\n", val);
+}
+
+static ssize_t writeback_batch_size_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u32 val;
+
+	if (kstrtouint(buf, 10, &val))
+		return -EINVAL;
+
+	if (!val)
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	zram->wb_batch_size = val;
+
+	return len;
+}
+
+static ssize_t writeback_batch_size_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	u32 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	guard(rwsem_read)(&zram->dev_lock);
+	val = zram->wb_batch_size;
+
+	return sysfs_emit(buf, "%u\n", val);
+}
+
+static void reset_bdev(struct zram *zram)
+{
+	if (!zram->backing_dev)
+		return;
+
+	/* hope filp_close flush all of IO */
+	filp_close(zram->backing_dev, NULL);
+	zram->backing_dev = NULL;
+	zram->bdev = NULL;
+	zram->disk->fops = &zram_devops;
+	kvfree(zram->bitmap);
+	zram->bitmap = NULL;
+}
+
+static ssize_t backing_dev_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct file *file;
+	struct zram *zram = dev_to_zram(dev);
+	char *p;
+	ssize_t ret;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	file = zram->backing_dev;
+	if (!file) {
+		memcpy(buf, "none\n", 5);
+		return 5;
+	}
+
+	p = file_path(file, buf, PAGE_SIZE - 1);
+	if (IS_ERR(p))
+		return PTR_ERR(p);
+
+	ret = strlen(p);
+	memmove(buf, p, ret);
+	buf[ret++] = '\n';
+	return ret;
+}
+
+static ssize_t backing_dev_store(struct device *dev,
+				 struct device_attribute *attr, const char *buf,
+				 size_t len)
+{
+	char *file_name;
+	size_t sz;
+	struct file *backing_dev = NULL;
+	struct inode *inode;
+	unsigned int bitmap_sz;
+	unsigned long nr_pages, *bitmap = NULL;
+	int err;
+	struct zram *zram = dev_to_zram(dev);
+
+	file_name = kmalloc(PATH_MAX, GFP_KERNEL);
+	if (!file_name)
+		return -ENOMEM;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram)) {
+		pr_info("Can't setup backing device for initialized device\n");
+		err = -EBUSY;
+		goto out;
+	}
+
+	strscpy(file_name, buf, PATH_MAX);
+	/* ignore trailing newline */
+	sz = strlen(file_name);
+	if (sz > 0 && file_name[sz - 1] == '\n')
+		file_name[sz - 1] = 0x00;
+
+	backing_dev = filp_open(file_name, O_RDWR | O_LARGEFILE | O_EXCL, 0);
+	if (IS_ERR(backing_dev)) {
+		err = PTR_ERR(backing_dev);
+		backing_dev = NULL;
+		goto out;
+	}
+
+	inode = backing_dev->f_mapping->host;
+
+	/* Support only block device in this moment */
+	if (!S_ISBLK(inode->i_mode)) {
+		err = -ENOTBLK;
+		goto out;
+	}
+
+	nr_pages = i_size_read(inode) >> PAGE_SHIFT;
+	/* Refuse to use zero sized device (also prevents self reference) */
+	if (!nr_pages) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	bitmap_sz = BITS_TO_LONGS(nr_pages) * sizeof(long);
+	bitmap = kvzalloc(bitmap_sz, GFP_KERNEL);
+	if (!bitmap) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	reset_bdev(zram);
+
+	zram->bdev = I_BDEV(inode);
+	zram->backing_dev = backing_dev;
+	zram->bitmap = bitmap;
+	zram->nr_pages = nr_pages;
+
+	pr_info("setup backing device %s\n", file_name);
+	kfree(file_name);
+
+	return len;
+out:
+	kvfree(bitmap);
+
+	if (backing_dev)
+		filp_close(backing_dev, NULL);
+
+	kfree(file_name);
+
+	return err;
+}
+
+static unsigned long zram_reserve_bdev_block(struct zram *zram)
+{
+	unsigned long blk_idx;
+
+	blk_idx = find_next_zero_bit(zram->bitmap, zram->nr_pages, 0);
+	if (blk_idx == zram->nr_pages)
+		return INVALID_BDEV_BLOCK;
+
+	set_bit(blk_idx, zram->bitmap);
+	atomic64_inc(&zram->stats.bd_count);
+	return blk_idx;
+}
+
+static void zram_release_bdev_block(struct zram *zram, unsigned long blk_idx)
+{
+	int was_set;
+
+	was_set = test_and_clear_bit(blk_idx, zram->bitmap);
+	WARN_ON_ONCE(!was_set);
+	atomic64_dec(&zram->stats.bd_count);
+}
+
+static void release_wb_req(struct zram_wb_req *req)
+{
+	__free_page(req->page);
+	kfree(req);
+}
+
+static void release_wb_ctl(struct zram_wb_ctl *wb_ctl)
+{
+	if (!wb_ctl)
+		return;
+
+	/* We should never have inflight requests at this point */
+	WARN_ON(atomic_read(&wb_ctl->num_inflight));
+	WARN_ON(!list_empty(&wb_ctl->done_reqs));
+
+	while (!list_empty(&wb_ctl->idle_reqs)) {
+		struct zram_wb_req *req;
+
+		req = list_first_entry(&wb_ctl->idle_reqs,
+				       struct zram_wb_req, entry);
+		list_del(&req->entry);
+		release_wb_req(req);
+	}
+
+	kfree_rcu(wb_ctl, rcu);
+}
+
+static struct zram_wb_ctl *init_wb_ctl(struct zram *zram)
+{
+	struct zram_wb_ctl *wb_ctl;
+	int i;
+
+	wb_ctl = kmalloc_obj(*wb_ctl);
+	if (!wb_ctl)
+		return NULL;
+
+	INIT_LIST_HEAD(&wb_ctl->idle_reqs);
+	INIT_LIST_HEAD(&wb_ctl->done_reqs);
+	atomic_set(&wb_ctl->num_inflight, 0);
+	init_waitqueue_head(&wb_ctl->done_wait);
+	spin_lock_init(&wb_ctl->done_lock);
+
+	for (i = 0; i < zram->wb_batch_size; i++) {
+		struct zram_wb_req *req;
+
+		/*
+		 * This is fatal condition only if we couldn't allocate
+		 * any requests at all.  Otherwise we just work with the
+		 * requests that we have successfully allocated, so that
+		 * writeback can still proceed, even if there is only one
+		 * request on the idle list.
+		 */
+		req = kzalloc_obj(*req, GFP_KERNEL | __GFP_NOWARN);
+		if (!req)
+			break;
+
+		req->page = alloc_page(GFP_KERNEL | __GFP_NOWARN);
+		if (!req->page) {
+			kfree(req);
+			break;
+		}
+
+		list_add(&req->entry, &wb_ctl->idle_reqs);
+	}
+
+	/* We couldn't allocate any requests, so writeabck is not possible */
+	if (list_empty(&wb_ctl->idle_reqs))
+		goto release_wb_ctl;
+
+	return wb_ctl;
+
+release_wb_ctl:
+	release_wb_ctl(wb_ctl);
+	return NULL;
+}
+
+static void zram_account_writeback_rollback(struct zram *zram)
+{
+	lockdep_assert_held_write(&zram->dev_lock);
+
+	if (zram->wb_limit_enable)
+		zram->bd_wb_limit +=  1UL << (PAGE_SHIFT - 12);
+}
+
+static void zram_account_writeback_submit(struct zram *zram)
+{
+	lockdep_assert_held_write(&zram->dev_lock);
+
+	if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
+		zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
+}
+
+static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
+{
+	unsigned long index = req->pps->index;
+	int err;
+
+	err = blk_status_to_errno(req->bio.bi_status);
+	if (err) {
+		/*
+		 * Failed wb requests should not be accounted in wb_limit
+		 * (if enabled).
+		 */
+		zram_account_writeback_rollback(zram);
+		zram_release_bdev_block(zram, req->blk_idx);
+		return err;
+	}
+
+	atomic64_inc(&zram->stats.bd_writes);
+	slot_lock(zram, index);
+	/*
+	 * We release slot lock during writeback so slot can change under us:
+	 * slot_free() or slot_free() and zram_write_page(). In both cases
+	 * slot loses ZRAM_PP_SLOT flag. No concurrent post-processing can
+	 * set ZRAM_PP_SLOT on such slots until current post-processing
+	 * finishes.
+	 */
+	if (!test_slot_flag(zram, index, ZRAM_PP_SLOT)) {
+		zram_release_bdev_block(zram, req->blk_idx);
+		goto out;
+	}
+
+	clear_slot_flag(zram, index, ZRAM_IDLE);
+	if (test_slot_flag(zram, index, ZRAM_HUGE))
+		atomic64_dec(&zram->stats.huge_pages);
+	atomic64_sub(get_slot_size(zram, index), &zram->stats.compr_data_size);
+	zs_free(zram->mem_pool, get_slot_handle(zram, index));
+	set_slot_handle(zram, index, req->blk_idx);
+	set_slot_flag(zram, index, ZRAM_WB);
+
+out:
+	slot_unlock(zram, index);
+	return 0;
+}
+
+static void zram_writeback_endio(struct bio *bio)
+{
+	struct zram_wb_req *req = container_of(bio, struct zram_wb_req, bio);
+	struct zram_wb_ctl *wb_ctl = bio->bi_private;
+	unsigned long flags;
+
+	rcu_read_lock();
+	spin_lock_irqsave(&wb_ctl->done_lock, flags);
+	list_add(&req->entry, &wb_ctl->done_reqs);
+	spin_unlock_irqrestore(&wb_ctl->done_lock, flags);
+
+	wake_up(&wb_ctl->done_wait);
+	rcu_read_unlock();
+}
+
+static void zram_submit_wb_request(struct zram *zram,
+				   struct zram_wb_ctl *wb_ctl,
+				   struct zram_wb_req *req)
+{
+	/*
+	 * wb_limit (if enabled) should be adjusted before submission,
+	 * so that we don't over-submit.
+	 */
+	zram_account_writeback_submit(zram);
+	atomic_inc(&wb_ctl->num_inflight);
+	req->bio.bi_private = wb_ctl;
+	submit_bio(&req->bio);
+}
+
+static int zram_complete_done_reqs(struct zram *zram,
+				   struct zram_wb_ctl *wb_ctl)
+{
+	struct zram_wb_req *req;
+	unsigned long flags;
+	int ret = 0, err;
+
+	while (atomic_read(&wb_ctl->num_inflight) > 0) {
+		spin_lock_irqsave(&wb_ctl->done_lock, flags);
+		req = list_first_entry_or_null(&wb_ctl->done_reqs,
+					       struct zram_wb_req, entry);
+		if (req)
+			list_del(&req->entry);
+		spin_unlock_irqrestore(&wb_ctl->done_lock, flags);
+
+		/* ->num_inflight > 0 doesn't mean we have done requests */
+		if (!req)
+			break;
+
+		err = zram_writeback_complete(zram, req);
+		if (err)
+			ret = err;
+
+		atomic_dec(&wb_ctl->num_inflight);
+		release_pp_slot(zram, req->pps);
+		req->pps = NULL;
+
+		list_add(&req->entry, &wb_ctl->idle_reqs);
+	}
+
+	return ret;
+}
+
+static struct zram_wb_req *zram_select_idle_req(struct zram_wb_ctl *wb_ctl)
+{
+	struct zram_wb_req *req;
+
+	req = list_first_entry_or_null(&wb_ctl->idle_reqs,
+				       struct zram_wb_req, entry);
+	if (req)
+		list_del(&req->entry);
+	return req;
+}
+
+static int zram_writeback_slots(struct zram *zram,
+				struct zram_pp_ctl *ctl,
+				struct zram_wb_ctl *wb_ctl)
+{
+	unsigned long blk_idx = INVALID_BDEV_BLOCK;
+	struct zram_wb_req *req = NULL;
+	struct zram_pp_slot *pps;
+	int ret = 0, err = 0;
+	unsigned long index = 0;
+
+	while ((pps = select_pp_slot(ctl))) {
+		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
+			ret = -EIO;
+			break;
+		}
+
+		while (!req) {
+			req = zram_select_idle_req(wb_ctl);
+			if (req)
+				break;
+
+			wait_event(wb_ctl->done_wait,
+				   !list_empty(&wb_ctl->done_reqs));
+
+			err = zram_complete_done_reqs(zram, wb_ctl);
+			/*
+			 * BIO errors are not fatal, we continue and simply
+			 * attempt to writeback the remaining objects (pages).
+			 * At the same time we need to signal user-space that
+			 * some writes (at least one, but also could be all of
+			 * them) were not successful and we do so by returning
+			 * the most recent BIO error.
+			 */
+			if (err)
+				ret = err;
+		}
+
+		if (blk_idx == INVALID_BDEV_BLOCK) {
+			blk_idx = zram_reserve_bdev_block(zram);
+			if (blk_idx == INVALID_BDEV_BLOCK) {
+				ret = -ENOSPC;
+				break;
+			}
+		}
+
+		index = pps->index;
+		slot_lock(zram, index);
+		/*
+		 * scan_slots() sets ZRAM_PP_SLOT and releases slot lock, so
+		 * slots can change in the meantime. If slots are accessed or
+		 * freed they lose ZRAM_PP_SLOT flag and hence we don't
+		 * post-process them.
+		 */
+		if (!test_slot_flag(zram, index, ZRAM_PP_SLOT))
+			goto next;
+		if (zram->compressed_wb)
+			err = read_from_zspool_raw(zram, req->page, index);
+		else
+			err = read_from_zspool(zram, req->page, index);
+		if (err)
+			goto next;
+		slot_unlock(zram, index);
+
+		/*
+		 * From now on pp-slot is owned by the req, remove it from
+		 * its pp bucket.
+		 */
+		list_del_init(&pps->entry);
+
+		req->blk_idx = blk_idx;
+		req->pps = pps;
+		bio_init(&req->bio, zram->bdev, &req->bio_vec, 1, REQ_OP_WRITE);
+		req->bio.bi_iter.bi_sector = req->blk_idx * (PAGE_SIZE >> 9);
+		req->bio.bi_end_io = zram_writeback_endio;
+		__bio_add_page(&req->bio, req->page, PAGE_SIZE, 0);
+
+		zram_submit_wb_request(zram, wb_ctl, req);
+		blk_idx = INVALID_BDEV_BLOCK;
+		req = NULL;
+		cond_resched();
+		continue;
+
+next:
+		slot_unlock(zram, index);
+		release_pp_slot(zram, pps);
+	}
+
+	/*
+	 * Selected idle req, but never submitted it due to some error or
+	 * wb limit.
+	 */
+	if (req)
+		release_wb_req(req);
+
+	if (blk_idx != INVALID_BDEV_BLOCK)
+		zram_release_bdev_block(zram, blk_idx);
+
+	while (atomic_read(&wb_ctl->num_inflight) > 0) {
+		wait_event(wb_ctl->done_wait, !list_empty(&wb_ctl->done_reqs));
+		err = zram_complete_done_reqs(zram, wb_ctl);
+		if (err)
+			ret = err;
+	}
+
+	return ret;
+}
+
+#define PAGE_WRITEBACK			0
+#define HUGE_WRITEBACK			(1 << 0)
+#define IDLE_WRITEBACK			(1 << 1)
+#define INCOMPRESSIBLE_WRITEBACK	(1 << 2)
+
+static int parse_page_index(char *val, unsigned long nr_pages,
+			    unsigned long *lo, unsigned long *hi)
+{
+	int ret;
+
+	ret = kstrtoul(val, 10, lo);
+	if (ret)
+		return ret;
+	if (*lo >= nr_pages)
+		return -ERANGE;
+	*hi = *lo + 1;
+	return 0;
+}
+
+static int parse_page_indexes(char *val, unsigned long nr_pages,
+			      unsigned long *lo, unsigned long *hi)
+{
+	char *delim;
+	int ret;
+
+	delim = strchr(val, '-');
+	if (!delim)
+		return -EINVAL;
+
+	*delim = 0x00;
+	ret = kstrtoul(val, 10, lo);
+	if (ret)
+		return ret;
+	if (*lo >= nr_pages)
+		return -ERANGE;
+
+	ret = kstrtoul(delim + 1, 10, hi);
+	if (ret)
+		return ret;
+	if (*hi >= nr_pages || *lo > *hi)
+		return -ERANGE;
+	*hi += 1;
+	return 0;
+}
+
+static int parse_mode(char *val, u32 *mode)
+{
+	*mode = 0;
+
+	if (!strcmp(val, "idle"))
+		*mode = IDLE_WRITEBACK;
+	if (!strcmp(val, "huge"))
+		*mode = HUGE_WRITEBACK;
+	if (!strcmp(val, "huge_idle"))
+		*mode = IDLE_WRITEBACK | HUGE_WRITEBACK;
+	if (!strcmp(val, "incompressible"))
+		*mode = INCOMPRESSIBLE_WRITEBACK;
+
+	if (*mode == 0)
+		return -EINVAL;
+	return 0;
+}
+
+static void scan_slots_for_writeback(struct zram *zram, u32 mode,
+				     unsigned long lo, unsigned long hi,
+				     struct zram_pp_ctl *ctl)
+{
+	unsigned long index = lo;
+
+	while (index < hi) {
+		bool ok = true;
+
+		slot_lock(zram, index);
+		if (!slot_allocated(zram, index))
+			goto next;
+
+		if (test_slot_flag(zram, index, ZRAM_WB) ||
+		    test_slot_flag(zram, index, ZRAM_SAME))
+			goto next;
+
+		if (mode & IDLE_WRITEBACK &&
+		    !test_slot_flag(zram, index, ZRAM_IDLE))
+			goto next;
+		if (mode & HUGE_WRITEBACK &&
+		    !test_slot_flag(zram, index, ZRAM_HUGE))
+			goto next;
+		if (mode & INCOMPRESSIBLE_WRITEBACK &&
+		    !test_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+			goto next;
+
+		ok = place_pp_slot(zram, ctl, index);
+next:
+		slot_unlock(zram, index);
+		if (!ok)
+			break;
+		index++;
+	}
+}
+
+static ssize_t writeback_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	unsigned long nr_pages;
+	unsigned long lo = 0, hi;
+	struct zram_pp_ctl *pp_ctl = NULL;
+	struct zram_wb_ctl *wb_ctl = NULL;
+	char *args, *param, *val;
+	ssize_t ret = len;
+	int err, mode = 0;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (!init_done(zram))
+		return -EINVAL;
+
+	if (!zram->backing_dev)
+		return -ENODEV;
+
+	nr_pages = zram->disksize >> PAGE_SHIFT;
+	hi = nr_pages;
+
+	pp_ctl = init_pp_ctl();
+	if (!pp_ctl)
+		return -ENOMEM;
+
+	wb_ctl = init_wb_ctl(zram);
+	if (!wb_ctl) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	args = skip_spaces(buf);
+	while (*args) {
+		args = next_arg(args, &param, &val);
+
+		/*
+		 * Workaround to support the old writeback interface.
+		 *
+		 * The old writeback interface has a minor inconsistency and
+		 * requires key=value only for page_index parameter, while the
+		 * writeback mode is a valueless parameter.
+		 *
+		 * This is not the case anymore and now all parameters are
+		 * required to have values, however, we need to support the
+		 * legacy writeback interface format so we check if we can
+		 * recognize a valueless parameter as the (legacy) writeback
+		 * mode.
+		 */
+		if (!val || !*val) {
+			err = parse_mode(param, &mode);
+			if (err) {
+				ret = err;
+				goto out;
+			}
+
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
+			break;
+		}
+
+		if (!strcmp(param, "type")) {
+			err = parse_mode(val, &mode);
+			if (err) {
+				ret = err;
+				goto out;
+			}
+
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
+			break;
+		}
+
+		if (!strcmp(param, "page_index")) {
+			err = parse_page_index(val, nr_pages, &lo, &hi);
+			if (err) {
+				ret = err;
+				goto out;
+			}
+
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
+			continue;
+		}
+
+		if (!strcmp(param, "page_indexes")) {
+			err = parse_page_indexes(val, nr_pages, &lo, &hi);
+			if (err) {
+				ret = err;
+				goto out;
+			}
+
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
+			continue;
+		}
+	}
+
+	err = zram_writeback_slots(zram, pp_ctl, wb_ctl);
+	if (err)
+		ret = err;
+
+out:
+	release_pp_ctl(zram, pp_ctl);
+	release_wb_ctl(wb_ctl);
+
+	return ret;
+}
+
+static int decompress_bdev_page(struct zram *zram, struct page *page,
+				unsigned long index)
+{
+	struct zcomp_strm *zstrm;
+	unsigned int size;
+	int ret, prio;
+	void *src;
+
+	slot_lock(zram, index);
+	/* Since slot was unlocked we need to make sure it's still ZRAM_WB */
+	if (!test_slot_flag(zram, index, ZRAM_WB)) {
+		slot_unlock(zram, index);
+		/* We read some stale data, zero it out */
+		memset_page(page, 0, 0, PAGE_SIZE);
+		return -EIO;
+	}
+
+	if (test_slot_flag(zram, index, ZRAM_HUGE)) {
+		slot_unlock(zram, index);
+		return 0;
+	}
+
+	size = get_slot_size(zram, index);
+	prio = get_slot_comp_priority(zram, index);
+
+	zstrm = zcomp_stream_get(zram->comps[prio]);
+	src = kmap_local_page(page);
+	ret = zcomp_decompress(zram->comps[prio], zstrm, src, size,
+			       zstrm->local_copy);
+	if (!ret)
+		copy_page(src, zstrm->local_copy);
+	kunmap_local(src);
+	zcomp_stream_put(zstrm);
+	slot_unlock(zram, index);
+
+	return ret;
+}
+
+static void zram_deferred_decompress(struct work_struct *w)
+{
+	struct zram_rb_req *req = container_of(w, struct zram_rb_req, work);
+	struct page *page = bio_first_page_all(req->bio);
+	struct zram *zram = req->zram;
+	unsigned long index = req->index;
+	int ret;
+
+	ret = decompress_bdev_page(zram, page, index);
+	if (ret)
+		req->parent->bi_status = BLK_STS_IOERR;
+
+	/* Decrement parent's ->remaining */
+	bio_endio(req->parent);
+	bio_put(req->bio);
+	kfree(req);
+}
+
+static void zram_async_read_endio(struct bio *bio)
+{
+	struct zram_rb_req *req = bio->bi_private;
+	struct zram *zram = req->zram;
+
+	if (bio->bi_status) {
+		req->parent->bi_status = bio->bi_status;
+		bio_endio(req->parent);
+		bio_put(bio);
+		kfree(req);
+		return;
+	}
+
+	/*
+	 * NOTE: zram_async_read_endio() is not exactly right place for this.
+	 * Ideally, we need to do it after ZRAM_WB check, but this requires
+	 * us to use wq path even on systems that don't enable compressed
+	 * writeback, because we cannot take slot-lock in the current context.
+	 *
+	 * Keep the existing behavior for now.
+	 */
+	if (zram->compressed_wb == false) {
+		/* No decompression needed, complete the parent IO */
+		bio_endio(req->parent);
+		bio_put(bio);
+		kfree(req);
+		return;
+	}
+
+	/*
+	 * zram decompression is sleepable, so we need to deffer it to
+	 * a preemptible context.
+	 */
+	INIT_WORK(&req->work, zram_deferred_decompress);
+	queue_work(system_highpri_wq, &req->work);
+}
+
+static int read_from_bdev_async(struct zram *zram, struct page *page,
+				unsigned long index, unsigned long blk_idx,
+				struct bio *parent)
+{
+	struct zram_rb_req *req;
+	struct bio *bio;
+
+	req = kmalloc_obj(*req, GFP_NOIO);
+	if (!req)
+		return -ENOMEM;
+
+	bio = bio_alloc(zram->bdev, 1, parent->bi_opf, GFP_NOIO);
+	if (!bio) {
+		kfree(req);
+		return -ENOMEM;
+	}
+
+	req->zram = zram;
+	req->index = index;
+	req->blk_idx = blk_idx;
+	req->bio = bio;
+	req->parent = parent;
+
+	bio->bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
+	bio->bi_private = req;
+	bio->bi_end_io = zram_async_read_endio;
+
+	__bio_add_page(bio, page, PAGE_SIZE, 0);
+	bio_inc_remaining(parent);
+	submit_bio(bio);
+
+	return 0;
+}
+
+static void zram_sync_read(struct work_struct *w)
+{
+	struct zram_rb_req *req = container_of(w, struct zram_rb_req, work);
+	struct bio_vec bv;
+	struct bio bio;
+
+	bio_init(&bio, req->zram->bdev, &bv, 1, REQ_OP_READ);
+	bio.bi_iter.bi_sector = req->blk_idx * (PAGE_SIZE >> 9);
+	__bio_add_page(&bio, req->page, PAGE_SIZE, 0);
+	req->error = submit_bio_wait(&bio);
+}
+
+/*
+ * Block layer want one ->submit_bio to be active at a time, so if we use
+ * chained IO with parent IO in same context, it's a deadlock. To avoid that,
+ * use a worker thread context.
+ */
+static int read_from_bdev_sync(struct zram *zram, struct page *page,
+			       unsigned long index, unsigned long blk_idx)
+{
+	struct zram_rb_req req;
+
+	req.page = page;
+	req.zram = zram;
+	req.blk_idx = blk_idx;
+
+	INIT_WORK_ONSTACK(&req.work, zram_sync_read);
+	queue_work(system_dfl_wq, &req.work);
+	flush_work(&req.work);
+	destroy_work_on_stack(&req.work);
+
+	if (req.error || zram->compressed_wb == false)
+		return req.error;
+
+	return decompress_bdev_page(zram, page, index);
+}
+
+static int read_from_bdev(struct zram *zram, struct page *page,
+			  unsigned long index, unsigned long blk_idx,
+			  struct bio *parent)
+{
+	atomic64_inc(&zram->stats.bd_reads);
+	if (!parent) {
+		if (WARN_ON_ONCE(!IS_ENABLED(ZRAM_PARTIAL_IO)))
+			return -EIO;
+		return read_from_bdev_sync(zram, page, index, blk_idx);
+	}
+	return read_from_bdev_async(zram, page, index, blk_idx, parent);
+}
+#else
+static inline void reset_bdev(struct zram *zram) {};
+static int read_from_bdev(struct zram *zram, struct page *page,
+			  unsigned long index, unsigned long blk_idx,
+			  struct bio *parent)
+{
+	return -EIO;
+}
+
+static void zram_release_bdev_block(struct zram *zram, unsigned long blk_idx)
+{
+}
+#endif
+
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+
+static struct dentry *zram_debugfs_root;
+
+static void zram_debugfs_create(void)
+{
+	zram_debugfs_root = debugfs_create_dir("zram", NULL);
+}
+
+static void zram_debugfs_destroy(void)
+{
+	debugfs_remove_recursive(zram_debugfs_root);
+}
+
+static ssize_t read_block_state(struct file *file, char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	char *kbuf;
+	unsigned long index;
+	ssize_t written = 0;
+	struct zram *zram = file->private_data;
+	unsigned long nr_pages;
+
+	kbuf = kvmalloc(count, GFP_KERNEL);
+	if (!kbuf)
+		return -ENOMEM;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	if (!init_done(zram)) {
+		kvfree(kbuf);
+		return -EINVAL;
+	}
+
+	nr_pages = zram->disksize >> PAGE_SHIFT;
+
+	for (index = *ppos; index < nr_pages; index++) {
+		int copied;
+
+		slot_lock(zram, index);
+		if (!slot_allocated(zram, index))
+			goto next;
+
+		copied = snprintf(kbuf + written, count,
+			"%12lu %12u.%06d %c%c%c%c%c%c\n",
+			index, zram->table[index].attr.ac_time, 0,
+			test_slot_flag(zram, index, ZRAM_SAME) ? 's' : '.',
+			test_slot_flag(zram, index, ZRAM_WB) ? 'w' : '.',
+			test_slot_flag(zram, index, ZRAM_HUGE) ? 'h' : '.',
+			test_slot_flag(zram, index, ZRAM_IDLE) ? 'i' : '.',
+			get_slot_comp_priority(zram, index) ? 'r' : '.',
+			test_slot_flag(zram, index,
+				       ZRAM_INCOMPRESSIBLE) ? 'n' : '.');
+
+		if (count <= copied) {
+			slot_unlock(zram, index);
+			break;
+		}
+		written += copied;
+		count -= copied;
+next:
+		slot_unlock(zram, index);
+		*ppos += 1;
+	}
+
+	if (copy_to_user(buf, kbuf, written))
+		written = -EFAULT;
+	kvfree(kbuf);
+
+	return written;
+}
+
+static const struct file_operations proc_zram_block_state_op = {
+	.open = simple_open,
+	.read = read_block_state,
+	.llseek = default_llseek,
+};
+
+static void zram_debugfs_register(struct zram *zram)
+{
+	if (!zram_debugfs_root)
+		return;
+
+	zram->debugfs_dir = debugfs_create_dir(zram->disk->disk_name,
+						zram_debugfs_root);
+	debugfs_create_file("block_state", 0400, zram->debugfs_dir,
+				zram, &proc_zram_block_state_op);
+}
+
+static void zram_debugfs_unregister(struct zram *zram)
+{
+	debugfs_remove_recursive(zram->debugfs_dir);
+}
+#else
+static void zram_debugfs_create(void) {};
+static void zram_debugfs_destroy(void) {};
+static void zram_debugfs_register(struct zram *zram) {};
+static void zram_debugfs_unregister(struct zram *zram) {};
+#endif
+
+/* Only algo parameter given, lookup by algo name */
+static int lookup_algo_priority(struct zram *zram, const char *algo,
+				u32 min_prio)
+{
+	s32 prio;
+
+	for (prio = min_prio; prio < ZRAM_MAX_COMPS; prio++) {
+		if (!zram->comp_algs[prio])
+			continue;
+
+		if (!strcmp(zram->comp_algs[prio], algo))
+			return prio;
+	}
+
+	return -EINVAL;
+}
+
+/* Both algo and priority parameters given, validate them */
+static int validate_algo_priority(struct zram *zram, const char *algo, u32 prio)
+{
+	if (prio >= ZRAM_MAX_COMPS)
+		return -EINVAL;
+	/* No algo at given priority */
+	if (!zram->comp_algs[prio])
+		return -EINVAL;
+	/* A different algo at given priority */
+	if (strcmp(zram->comp_algs[prio], algo))
+		return -EINVAL;
+	return 0;
+}
+
+static void comp_algorithm_set(struct zram *zram, u32 prio, const char *alg)
+{
+	zram->comp_algs[prio] = alg;
+}
+
+static void comp_params_reset(struct zram *zram, u32 prio)
+{
+	struct zcomp_params *params = &zram->params[prio];
+
+	vfree(params->dict);
+	params->level = ZCOMP_PARAM_NOT_SET;
+	params->deflate.winbits = ZCOMP_PARAM_NOT_SET;
+	params->dict_sz = 0;
+	params->dict = NULL;
+}
+
+static int __comp_algorithm_store(struct zram *zram, u32 prio, const char *buf)
+{
+	const char *alg;
+	size_t sz;
+
+	sz = strlen(buf);
+	if (sz >= ZRAM_MAX_ALGO_NAME_SZ)
+		return -E2BIG;
+
+	alg = zcomp_lookup_backend_name(buf);
+	if (!alg)
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram)) {
+		pr_info("Can't change algorithm for initialized device\n");
+		return -EBUSY;
+	}
+
+	comp_algorithm_set(zram, prio, alg);
+	comp_params_reset(zram, prio);
+	return 0;
+}
+
+static int comp_params_store(struct zram *zram, u32 prio, s32 level,
+			     const char *dict_path,
+			     struct deflate_params *deflate_params)
+{
+	ssize_t sz = 0;
+
+	comp_params_reset(zram, prio);
+
+	if (dict_path) {
+		sz = kernel_read_file_from_path(dict_path, 0,
+						&zram->params[prio].dict,
+						INT_MAX,
+						NULL,
+						READING_POLICY);
+		if (sz < 0) {
+			pr_err("failed to load dictionary %s (err=%zd)\n",
+			       dict_path, sz);
+			return sz;
+		}
+		if (sz == 0) {
+			pr_err("failed to load dictionary %s (empty file)\n",
+			       dict_path);
+			return -EINVAL;
+		}
+	}
+
+	zram->params[prio].dict_sz = sz;
+	zram->params[prio].level = level;
+	zram->params[prio].deflate.winbits = deflate_params->winbits;
+	return 0;
+}
+
+static ssize_t algorithm_params_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t len)
+{
+	s32 prio = ZRAM_PRIMARY_COMP, level = ZCOMP_PARAM_NOT_SET;
+	char *args, *param, *val, *algo = NULL, *dict_path = NULL;
+	struct deflate_params deflate_params;
+	struct zram *zram = dev_to_zram(dev);
+	bool prio_param = false;
+	int ret;
+
+	deflate_params.winbits = ZCOMP_PARAM_NOT_SET;
+
+	args = skip_spaces(buf);
+	while (*args) {
+		args = next_arg(args, &param, &val);
+
+		if (!val || !*val)
+			return -EINVAL;
+
+		if (!strcmp(param, "priority")) {
+			prio_param = true;
+			ret = kstrtoint(val, 10, &prio);
+			if (ret)
+				return ret;
+			continue;
+		}
+
+		if (!strcmp(param, "level")) {
+			ret = kstrtoint(val, 10, &level);
+			if (ret)
+				return ret;
+			continue;
+		}
+
+		if (!strcmp(param, "algo")) {
+			algo = val;
+			continue;
+		}
+
+		if (!strcmp(param, "dict")) {
+			dict_path = val;
+			continue;
+		}
+
+		if (!strcmp(param, "deflate.winbits")) {
+			ret = kstrtoint(val, 10, &deflate_params.winbits);
+			if (ret)
+				return ret;
+			continue;
+		}
+	}
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram))
+		return -EBUSY;
+
+	if (prio_param) {
+		if (prio < ZRAM_PRIMARY_COMP || prio >= ZRAM_MAX_COMPS)
+			return -EINVAL;
+	}
+
+	if (algo && prio_param) {
+		ret = validate_algo_priority(zram, algo, prio);
+		if (ret)
+			return ret;
+	}
+
+	if (algo && !prio_param) {
+		prio = lookup_algo_priority(zram, algo, ZRAM_PRIMARY_COMP);
+		if (prio < 0)
+			return -EINVAL;
+	}
+
+	ret = comp_params_store(zram, prio, level, dict_path, &deflate_params);
+	return ret ? ret : len;
+}
+
+static ssize_t comp_algorithm_show(struct device *dev,
+				   struct device_attribute *attr,
+				   char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t sz;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	sz = zcomp_available_show(zram->comp_algs[ZRAM_PRIMARY_COMP], buf, 0);
+	return sz;
+}
+
+static ssize_t comp_algorithm_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf,
+				    size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = __comp_algorithm_store(zram, ZRAM_PRIMARY_COMP, buf);
+	return ret ? ret : len;
+}
+
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static ssize_t recomp_algorithm_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t sz = 0;
+	u32 prio;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	for (prio = ZRAM_SECONDARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
+		if (!zram->comp_algs[prio])
+			continue;
+
+		sz += sysfs_emit_at(buf, sz, "#%d: ", prio);
+		sz += zcomp_available_show(zram->comp_algs[prio], buf, sz);
+	}
+	return sz;
+}
+
+static ssize_t recomp_algorithm_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int prio = ZRAM_SECONDARY_COMP;
+	char *args, *param, *val;
+	char *alg = NULL;
+	int ret;
+
+	args = skip_spaces(buf);
+	while (*args) {
+		args = next_arg(args, &param, &val);
+
+		if (!val || !*val)
+			return -EINVAL;
+
+		if (!strcmp(param, "algo")) {
+			alg = val;
+			continue;
+		}
+
+		if (!strcmp(param, "priority")) {
+			ret = kstrtoint(val, 10, &prio);
+			if (ret)
+				return ret;
+			continue;
+		}
+	}
+
+	if (!alg)
+		return -EINVAL;
+
+	if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS)
+		return -EINVAL;
+
+	ret = __comp_algorithm_store(zram, prio, alg);
+	return ret ? ret : len;
+}
+#endif
+
+static ssize_t compact_store(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	guard(rwsem_read)(&zram->dev_lock);
+	if (!init_done(zram))
+		return -EINVAL;
+
+	zs_compact(zram->mem_pool);
+
+	return len;
+}
+
+static ssize_t io_stat_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	ret = sysfs_emit(buf,
+			"%8llu %8llu 0 %8llu\n",
+			(u64)atomic64_read(&zram->stats.failed_reads),
+			(u64)atomic64_read(&zram->stats.failed_writes),
+			(u64)atomic64_read(&zram->stats.notify_free));
+
+	return ret;
+}
+
+static ssize_t mm_stat_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+	struct zs_pool_stats pool_stats;
+	u64 orig_size, mem_used = 0;
+	long max_used;
+	ssize_t ret;
+
+	memset(&pool_stats, 0x00, sizeof(struct zs_pool_stats));
+
+	guard(rwsem_read)(&zram->dev_lock);
+	if (init_done(zram)) {
+		mem_used = zs_get_total_pages(zram->mem_pool);
+		zs_pool_stats(zram->mem_pool, &pool_stats);
+	}
+
+	orig_size = atomic64_read(&zram->stats.pages_stored);
+	max_used = atomic_long_read(&zram->stats.max_used_pages);
+
+	ret = sysfs_emit(buf,
+			"%8llu %8llu %8llu %8lu %8ld %8llu %8lu %8llu %8llu\n",
+			orig_size << PAGE_SHIFT,
+			(u64)atomic64_read(&zram->stats.compr_data_size),
+			mem_used << PAGE_SHIFT,
+			zram->limit_pages << PAGE_SHIFT,
+			max_used << PAGE_SHIFT,
+			(u64)atomic64_read(&zram->stats.same_pages),
+			atomic_long_read(&pool_stats.pages_compacted),
+			(u64)atomic64_read(&zram->stats.huge_pages),
+			(u64)atomic64_read(&zram->stats.huge_pages_since));
+
+	return ret;
+}
+
+static ssize_t debug_stat_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	int version = 1;
+	struct zram *zram = dev_to_zram(dev);
+	ssize_t ret;
+
+	guard(rwsem_read)(&zram->dev_lock);
+	ret = sysfs_emit(buf,
+			"version: %d\n0 %8llu\n",
+			version,
+			(u64)atomic64_read(&zram->stats.miss_free));
+
+	return ret;
+}
+
+static void zram_meta_free(struct zram *zram, u64 disksize)
+{
+	unsigned long num_pages = disksize >> PAGE_SHIFT;
+	unsigned long index;
+
+	if (!zram->table)
+		return;
+
+	/* Free all pages that are still in this zram device */
+	for (index = 0; index < num_pages; index++)
+		slot_free(zram, index);
+
+	zs_destroy_pool(zram->mem_pool);
+	vfree(zram->table);
+	zram->table = NULL;
+	lockdep_unregister_key(&zram->table_lock_key);
+}
+
+static bool zram_meta_alloc(struct zram *zram, u64 disksize)
+{
+	unsigned long num_pages;
+
+	num_pages = disksize >> PAGE_SHIFT;
+	zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table)));
+	if (!zram->table)
+		return false;
+
+	zram->mem_pool = zs_create_pool(zram->disk->disk_name);
+	if (!zram->mem_pool) {
+		vfree(zram->table);
+		zram->table = NULL;
+		return false;
+	}
+
+	if (!huge_class_size)
+		huge_class_size = zs_huge_class_size(zram->mem_pool);
+
+	lockdep_register_key(&zram->table_lock_key);
+	lockdep_init_map(&zram->table_lock_map, "zram->table[index].lock", &zram->table_lock_key, 0);
+
+	return true;
+}
+
+static void slot_free(struct zram *zram, unsigned long index)
+{
+	unsigned long handle;
+
+#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
+	zram->table[index].attr.ac_time = 0;
+#endif
+
+	clear_slot_flag(zram, index, ZRAM_IDLE);
+	clear_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+	clear_slot_flag(zram, index, ZRAM_PP_SLOT);
+	set_slot_comp_priority(zram, index, 0);
+
+	if (test_slot_flag(zram, index, ZRAM_HUGE)) {
+		/*
+		 * Writeback completion decrements ->huge_pages but keeps
+		 * ZRAM_HUGE flag for deferred decompression path.
+		 */
+		if (!test_slot_flag(zram, index, ZRAM_WB))
+			atomic64_dec(&zram->stats.huge_pages);
+		clear_slot_flag(zram, index, ZRAM_HUGE);
+	}
+
+	if (test_slot_flag(zram, index, ZRAM_WB)) {
+		clear_slot_flag(zram, index, ZRAM_WB);
+		zram_release_bdev_block(zram, get_slot_handle(zram, index));
+		goto out;
+	}
+
+	/*
+	 * No memory is allocated for same element filled pages.
+	 * Simply clear same page flag.
+	 */
+	if (test_slot_flag(zram, index, ZRAM_SAME)) {
+		clear_slot_flag(zram, index, ZRAM_SAME);
+		atomic64_dec(&zram->stats.same_pages);
+		goto out;
+	}
+
+	handle = get_slot_handle(zram, index);
+	if (!handle)
+		return;
+
+	zs_free(zram->mem_pool, handle);
+
+	atomic64_sub(get_slot_size(zram, index),
+		     &zram->stats.compr_data_size);
+out:
+	atomic64_dec(&zram->stats.pages_stored);
+	set_slot_handle(zram, index, 0);
+	set_slot_size(zram, index, 0);
+}
+
+static int read_same_filled_page(struct zram *zram, struct page *page,
+				 unsigned long index)
+{
+	void *mem;
+
+	mem = kmap_local_page(page);
+	zram_fill_page(mem, PAGE_SIZE, get_slot_handle(zram, index));
+	kunmap_local(mem);
+	return 0;
+}
+
+static int read_incompressible_page(struct zram *zram, struct page *page,
+				    unsigned long index)
+{
+	unsigned long handle;
+	void *src, *dst;
+
+	handle = get_slot_handle(zram, index);
+	src = zs_obj_read_begin(zram->mem_pool, handle, PAGE_SIZE, NULL);
+	dst = kmap_local_page(page);
+	copy_page(dst, src);
+	kunmap_local(dst);
+	zs_obj_read_end(zram->mem_pool, handle, PAGE_SIZE, src);
+
+	return 0;
+}
+
+static int read_compressed_page(struct zram *zram, struct page *page,
+				unsigned long index)
+{
+	struct zcomp_strm *zstrm;
+	unsigned long handle;
+	unsigned int size;
+	void *src, *dst;
+	int ret, prio;
+
+	handle = get_slot_handle(zram, index);
+	size = get_slot_size(zram, index);
+	prio = get_slot_comp_priority(zram, index);
+
+	zstrm = zcomp_stream_get(zram->comps[prio]);
+	src = zs_obj_read_begin(zram->mem_pool, handle, size,
+				zstrm->local_copy);
+	dst = kmap_local_page(page);
+	ret = zcomp_decompress(zram->comps[prio], zstrm, src, size, dst);
+	kunmap_local(dst);
+	zs_obj_read_end(zram->mem_pool, handle, size, src);
+	zcomp_stream_put(zstrm);
+
+	return ret;
+}
+
+#if defined CONFIG_ZRAM_WRITEBACK
+static int read_from_zspool_raw(struct zram *zram, struct page *page,
+				unsigned long index)
+{
+	struct zcomp_strm *zstrm;
+	unsigned long handle;
+	unsigned int size;
+	void *src;
+
+	handle = get_slot_handle(zram, index);
+	size = get_slot_size(zram, index);
+
+	/*
+	 * We need to get stream just for ->local_copy buffer, in
+	 * case if object spans two physical pages. No decompression
+	 * takes place here, as we read raw compressed data.
+	 */
+	zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
+	src = zs_obj_read_begin(zram->mem_pool, handle, size,
+				zstrm->local_copy);
+	memcpy_to_page(page, 0, src, size);
+	zs_obj_read_end(zram->mem_pool, handle, size, src);
+	zcomp_stream_put(zstrm);
+
+	memzero_page(page, size, PAGE_SIZE - size);
+
+	return 0;
+}
+#endif
+
+/*
+ * Reads (decompresses if needed) a page from zspool (zsmalloc).
+ * Corresponding ZRAM slot should be locked.
+ */
+static int read_from_zspool(struct zram *zram, struct page *page,
+			    unsigned long index)
+{
+	if (test_slot_flag(zram, index, ZRAM_SAME) ||
+	    !get_slot_handle(zram, index))
+		return read_same_filled_page(zram, page, index);
+
+	if (!test_slot_flag(zram, index, ZRAM_HUGE))
+		return read_compressed_page(zram, page, index);
+	else
+		return read_incompressible_page(zram, page, index);
+}
+
+static int zram_read_page(struct zram *zram, struct page *page,
+			  unsigned long index, struct bio *parent)
+{
+	int ret;
+
+	slot_lock(zram, index);
+	if (!test_slot_flag(zram, index, ZRAM_WB)) {
+		/* Slot should be locked through out the function call */
+		ret = read_from_zspool(zram, page, index);
+		slot_unlock(zram, index);
+	} else {
+		unsigned long blk_idx = get_slot_handle(zram, index);
+
+		/*
+		 * The slot should be unlocked before reading from the backing
+		 * device.
+		 */
+		slot_unlock(zram, index);
+		ret = read_from_bdev(zram, page, index, blk_idx, parent);
+	}
+
+	/* Should NEVER happen. Return bio error if it does. */
+	if (WARN_ON(ret < 0))
+		pr_err("Decompression failed! err=%d, page=%lu\n", ret, index);
+
+	return ret;
+}
+
+/*
+ * Use a temporary buffer to decompress the page, as the decompressor
+ * always expects a full page for the output.
+ */
+static int zram_bvec_read_partial(struct zram *zram, struct bio_vec *bvec,
+				  unsigned long index, int offset)
+{
+	struct page *page = alloc_page(GFP_NOIO);
+	int ret;
+
+	if (!page)
+		return -ENOMEM;
+	ret = zram_read_page(zram, page, index, NULL);
+	if (likely(!ret))
+		memcpy_to_bvec(bvec, page_address(page) + offset);
+	__free_page(page);
+	return ret;
+}
+
+static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
+			  unsigned long index, int offset, struct bio *bio)
+{
+	if (is_partial_io(bvec))
+		return zram_bvec_read_partial(zram, bvec, index, offset);
+	return zram_read_page(zram, bvec->bv_page, index, bio);
+}
+
+static int write_same_filled_page(struct zram *zram, unsigned long fill,
+				  unsigned long index)
+{
+	slot_lock(zram, index);
+	slot_free(zram, index);
+	set_slot_flag(zram, index, ZRAM_SAME);
+	set_slot_handle(zram, index, fill);
+	slot_unlock(zram, index);
+
+	atomic64_inc(&zram->stats.same_pages);
+	atomic64_inc(&zram->stats.pages_stored);
+
+	return 0;
+}
+
+static int write_incompressible_page(struct zram *zram, struct page *page,
+				     unsigned long index)
+{
+	unsigned long handle;
+	void *src;
+
+	/*
+	 * This function is called from preemptible context so we don't need
+	 * to do optimistic and fallback to pessimistic handle allocation,
+	 * like we do for compressible pages.
+	 */
+	handle = zs_malloc(zram->mem_pool, PAGE_SIZE,
+			   GFP_NOIO | __GFP_NOWARN |
+			   __GFP_HIGHMEM | __GFP_MOVABLE, page_to_nid(page));
+	if (IS_ERR_VALUE(handle))
+		return PTR_ERR((void *)handle);
+
+	if (!zram_can_store_page(zram)) {
+		zs_free(zram->mem_pool, handle);
+		return -ENOMEM;
+	}
+
+	src = kmap_local_page(page);
+	zs_obj_write(zram->mem_pool, handle, src, PAGE_SIZE);
+	kunmap_local(src);
+
+	slot_lock(zram, index);
+	slot_free(zram, index);
+	set_slot_flag(zram, index, ZRAM_HUGE);
+	set_slot_handle(zram, index, handle);
+	set_slot_size(zram, index, PAGE_SIZE);
+	slot_unlock(zram, index);
+
+	atomic64_add(PAGE_SIZE, &zram->stats.compr_data_size);
+	atomic64_inc(&zram->stats.huge_pages);
+	atomic64_inc(&zram->stats.huge_pages_since);
+	atomic64_inc(&zram->stats.pages_stored);
+
+	return 0;
+}
+
+static int zram_write_page(struct zram *zram, struct page *page,
+			   unsigned long index)
+{
+	int ret = 0;
+	unsigned long handle;
+	unsigned int comp_len;
+	void *mem;
+	struct zcomp_strm *zstrm;
+	unsigned long element;
+	bool same_filled;
+
+	mem = kmap_local_page(page);
+	same_filled = page_same_filled(mem, &element);
+	kunmap_local(mem);
+	if (same_filled)
+		return write_same_filled_page(zram, element, index);
+
+	zstrm = zcomp_stream_get(zram->comps[ZRAM_PRIMARY_COMP]);
+	mem = kmap_local_page(page);
+	ret = zcomp_compress(zram->comps[ZRAM_PRIMARY_COMP], zstrm,
+			     mem, &comp_len);
+	kunmap_local(mem);
+
+	if (unlikely(ret)) {
+		zcomp_stream_put(zstrm);
+		pr_err("Compression failed! err=%d\n", ret);
+		return ret;
+	}
+
+	if (comp_len >= huge_class_size) {
+		zcomp_stream_put(zstrm);
+		return write_incompressible_page(zram, page, index);
+	}
+
+	handle = zs_malloc(zram->mem_pool, comp_len,
+			   GFP_NOIO | __GFP_NOWARN |
+			   __GFP_HIGHMEM | __GFP_MOVABLE, page_to_nid(page));
+	if (IS_ERR_VALUE(handle)) {
+		zcomp_stream_put(zstrm);
+		return PTR_ERR((void *)handle);
+	}
+
+	if (!zram_can_store_page(zram)) {
+		zcomp_stream_put(zstrm);
+		zs_free(zram->mem_pool, handle);
+		return -ENOMEM;
+	}
+
+	zs_obj_write(zram->mem_pool, handle, zstrm->buffer, comp_len);
+	zcomp_stream_put(zstrm);
+
+	slot_lock(zram, index);
+	slot_free(zram, index);
+	set_slot_handle(zram, index, handle);
+	set_slot_size(zram, index, comp_len);
+	slot_unlock(zram, index);
+
+	/* Update stats */
+	atomic64_inc(&zram->stats.pages_stored);
+	atomic64_add(comp_len, &zram->stats.compr_data_size);
+
+	return ret;
+}
+
+/*
+ * This is a partial IO. Read the full page before writing the changes.
+ */
+static int zram_bvec_write_partial(struct zram *zram, struct bio_vec *bvec,
+				   unsigned long index, int offset)
+{
+	struct page *page = alloc_page(GFP_NOIO);
+	int ret;
+
+	if (!page)
+		return -ENOMEM;
+
+	ret = zram_read_page(zram, page, index, NULL);
+	if (!ret) {
+		memcpy_from_bvec(page_address(page) + offset, bvec);
+		ret = zram_write_page(zram, page, index);
+	}
+	__free_page(page);
+	return ret;
+}
+
+static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
+			   unsigned long index, int offset)
+{
+	if (is_partial_io(bvec))
+		return zram_bvec_write_partial(zram, bvec, index, offset);
+	return zram_write_page(zram, bvec->bv_page, index);
+}
+
+#ifdef CONFIG_ZRAM_MULTI_COMP
+#define RECOMPRESS_IDLE		(1 << 0)
+#define RECOMPRESS_HUGE		(1 << 1)
+
+static bool highest_priority_algorithm(struct zram *zram, u32 prio)
+{
+	u32 p;
+
+	for (p = prio + 1; p < ZRAM_MAX_COMPS; p++) {
+		if (zram->comp_algs[p])
+			return false;
+	}
+
+	return true;
+}
+
+static void scan_slots_for_recompress(struct zram *zram, u32 mode, u32 prio,
+				      struct zram_pp_ctl *ctl)
+{
+	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	unsigned long index;
+
+	for (index = 0; index < nr_pages; index++) {
+		bool ok = true;
+
+		slot_lock(zram, index);
+		if (!slot_allocated(zram, index))
+			goto next;
+
+		if (mode & RECOMPRESS_IDLE &&
+		    !test_slot_flag(zram, index, ZRAM_IDLE))
+			goto next;
+
+		if (mode & RECOMPRESS_HUGE &&
+		    !test_slot_flag(zram, index, ZRAM_HUGE))
+			goto next;
+
+		if (test_slot_flag(zram, index, ZRAM_WB) ||
+		    test_slot_flag(zram, index, ZRAM_SAME) ||
+		    test_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE))
+			goto next;
+
+		/* Already compressed with same or higher priority */
+		if (get_slot_comp_priority(zram, index) >= prio)
+			goto next;
+
+		ok = place_pp_slot(zram, ctl, index);
+next:
+		slot_unlock(zram, index);
+		if (!ok)
+			break;
+	}
+}
+
+/*
+ * This function will decompress (unless it's ZRAM_HUGE) the page and then
+ * attempt to compress it using provided compression algorithm priority
+ * (which is potentially more effective).
+ *
+ * Corresponding ZRAM slot should be locked.
+ */
+static int recompress_slot(struct zram *zram, unsigned long index,
+			   struct page *page, u64 *num_recomp_pages,
+			   u32 threshold, u32 prio)
+{
+	struct zcomp_strm *zstrm = NULL;
+	unsigned long handle_old;
+	unsigned long handle_new;
+	unsigned int comp_len_old;
+	unsigned int comp_len_new;
+	unsigned int class_index_old;
+	unsigned int class_index_new;
+	void *src;
+	int ret = 0;
+
+	handle_old = get_slot_handle(zram, index);
+	if (!handle_old)
+		return -EINVAL;
+
+	comp_len_old = get_slot_size(zram, index);
+	/*
+	 * Do not recompress objects that are already "small enough".
+	 */
+	if (comp_len_old < threshold)
+		return 0;
+
+	ret = read_from_zspool(zram, page, index);
+	if (ret)
+		return ret;
+
+	/*
+	 * We touched this entry so mark it as non-IDLE. This makes sure that
+	 * we don't preserve IDLE flag and don't incorrectly pick this entry
+	 * for different post-processing type (e.g. writeback).
+	 */
+	clear_slot_flag(zram, index, ZRAM_IDLE);
+
+	zstrm = zcomp_stream_get(zram->comps[prio]);
+	src = kmap_local_page(page);
+	ret = zcomp_compress(zram->comps[prio], zstrm, src, &comp_len_new);
+	kunmap_local(src);
+
+	/*
+	 * Decrement the limit (if set) on pages we can recompress, even
+	 * when current recompression was unsuccessful or did not compress
+	 * the page below the threshold, because we still spent resources
+	 * on it.
+	 */
+	if (*num_recomp_pages)
+		*num_recomp_pages -= 1;
+
+	if (ret) {
+		zcomp_stream_put(zstrm);
+		return ret;
+	}
+
+	class_index_old = zs_lookup_class_index(zram->mem_pool, comp_len_old);
+	class_index_new = zs_lookup_class_index(zram->mem_pool, comp_len_new);
+
+	if (class_index_new >= class_index_old ||
+	    (threshold && comp_len_new >= threshold)) {
+		zcomp_stream_put(zstrm);
+
+		/*
+		 * Secondary algorithms failed to re-compress the page
+		 * in a way that would save memory.
+		 *
+		 * Mark the object incompressible if the max-priority (the
+		 * last configured one) algorithm couldn't re-compress it.
+		 */
+		if (highest_priority_algorithm(zram, prio))
+			set_slot_flag(zram, index, ZRAM_INCOMPRESSIBLE);
+		return 0;
+	}
+
+	/*
+	 * We are holding per-CPU stream mutex and entry lock so better
+	 * avoid direct reclaim.  Allocation error is not fatal since
+	 * we still have the old object in the mem_pool.
+	 *
+	 * XXX: technically, the node we really want here is the node that
+	 * holds the original compressed data. But that would require us to
+	 * modify zsmalloc API to return this information. For now, we will
+	 * make do with the node of the page allocated for recompression.
+	 */
+	handle_new = zs_malloc(zram->mem_pool, comp_len_new,
+			       GFP_NOIO | __GFP_NOWARN |
+			       __GFP_HIGHMEM | __GFP_MOVABLE,
+			       page_to_nid(page));
+	if (IS_ERR_VALUE(handle_new)) {
+		zcomp_stream_put(zstrm);
+		return PTR_ERR((void *)handle_new);
+	}
+
+	zs_obj_write(zram->mem_pool, handle_new, zstrm->buffer, comp_len_new);
+	zcomp_stream_put(zstrm);
+
+	slot_free(zram, index);
+	set_slot_handle(zram, index, handle_new);
+	set_slot_size(zram, index, comp_len_new);
+	set_slot_comp_priority(zram, index, prio);
+
+	atomic64_add(comp_len_new, &zram->stats.compr_data_size);
+	atomic64_inc(&zram->stats.pages_stored);
+
+	return 0;
+}
+
+static ssize_t recompress_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	char *args, *param, *val, *algo = NULL;
+	u64 num_recomp_pages = ULLONG_MAX;
+	struct zram_pp_ctl *ctl = NULL;
+	s32 prio = ZRAM_SECONDARY_COMP;
+	u32 mode = 0, threshold = 0;
+	struct zram_pp_slot *pps;
+	struct page *page = NULL;
+	bool prio_param = false;
+	ssize_t ret;
+
+	args = skip_spaces(buf);
+	while (*args) {
+		args = next_arg(args, &param, &val);
+
+		if (!val || !*val)
+			return -EINVAL;
+
+		if (!strcmp(param, "type")) {
+			if (!strcmp(val, "idle"))
+				mode = RECOMPRESS_IDLE;
+			if (!strcmp(val, "huge"))
+				mode = RECOMPRESS_HUGE;
+			if (!strcmp(val, "huge_idle"))
+				mode = RECOMPRESS_IDLE | RECOMPRESS_HUGE;
+			if (!mode)
+				return -EINVAL;
+			continue;
+		}
+
+		if (!strcmp(param, "max_pages")) {
+			/*
+			 * Limit the number of entries (pages) we attempt to
+			 * recompress.
+			 */
+			ret = kstrtoull(val, 10, &num_recomp_pages);
+			if (ret)
+				return ret;
+			continue;
+		}
+
+		if (!strcmp(param, "threshold")) {
+			/*
+			 * We will re-compress only idle objects equal or
+			 * greater in size than watermark.
+			 */
+			ret = kstrtouint(val, 10, &threshold);
+			if (ret)
+				return ret;
+			continue;
+		}
+
+		if (!strcmp(param, "algo")) {
+			algo = val;
+			continue;
+		}
+
+		if (!strcmp(param, "priority")) {
+			prio_param = true;
+			ret = kstrtoint(val, 10, &prio);
+			if (ret)
+				return ret;
+			continue;
+		}
+	}
+
+	if (threshold >= huge_class_size)
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (!init_done(zram))
+		return -EINVAL;
+
+	if (prio_param) {
+		if (prio < ZRAM_SECONDARY_COMP || prio >= ZRAM_MAX_COMPS)
+			return -EINVAL;
+	}
+
+	if (algo && prio_param) {
+		ret = validate_algo_priority(zram, algo, prio);
+		if (ret)
+			return ret;
+	}
+
+	if (algo && !prio_param) {
+		prio = lookup_algo_priority(zram, algo, ZRAM_SECONDARY_COMP);
+		if (prio < 0)
+			return -EINVAL;
+	}
+
+	if (!zram->comps[prio])
+		return -EINVAL;
+
+	page = alloc_page(GFP_KERNEL);
+	if (!page) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ctl = init_pp_ctl();
+	if (!ctl) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	scan_slots_for_recompress(zram, mode, prio, ctl);
+
+	ret = len;
+	while ((pps = select_pp_slot(ctl))) {
+		int err = 0;
+
+		if (!num_recomp_pages)
+			break;
+
+		slot_lock(zram, pps->index);
+		if (!test_slot_flag(zram, pps->index, ZRAM_PP_SLOT))
+			goto next;
+
+		err = recompress_slot(zram, pps->index, page,
+				      &num_recomp_pages, threshold, prio);
+next:
+		slot_unlock(zram, pps->index);
+		release_pp_slot(zram, pps);
+
+		if (err) {
+			ret = err;
+			break;
+		}
+
+		cond_resched();
+	}
+
+out:
+	if (page)
+		__free_page(page);
+	release_pp_ctl(zram, ctl);
+	return ret;
+}
+#endif
+
+static void zram_bio_discard(struct zram *zram, struct bio *bio)
+{
+	size_t n = bio->bi_iter.bi_size;
+	unsigned long index = bio->bi_iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+	u32 offset = (bio->bi_iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+			SECTOR_SHIFT;
+
+	/*
+	 * zram manages data in physical block size units. Because logical block
+	 * size isn't identical with physical block size on some arch, we
+	 * could get a discard request pointing to a specific offset within a
+	 * certain physical block.  Although we can handle this request by
+	 * reading that physiclal block and decompressing and partially zeroing
+	 * and re-compressing and then re-storing it, this isn't reasonable
+	 * because our intent with a discard request is to save memory.  So
+	 * skipping this logical block is appropriate here.
+	 */
+	if (offset) {
+		if (n <= (PAGE_SIZE - offset))
+			goto end_bio;
+
+		n -= (PAGE_SIZE - offset);
+		index++;
+	}
+
+	while (n >= PAGE_SIZE) {
+		slot_lock(zram, index);
+		slot_free(zram, index);
+		slot_unlock(zram, index);
+		atomic64_inc(&zram->stats.notify_free);
+		index++;
+		n -= PAGE_SIZE;
+	}
+
+end_bio:
+	bio_endio(bio);
+}
+
+static void zram_bio_read(struct zram *zram, struct bio *bio)
+{
+	unsigned long start_time = bio_start_io_acct(bio);
+	struct bvec_iter iter = bio->bi_iter;
+
+	do {
+		unsigned long index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+				SECTOR_SHIFT;
+		struct bio_vec bv = bio_iter_iovec(bio, iter);
+
+		bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);
+
+		if (zram_bvec_read(zram, &bv, index, offset, bio) < 0) {
+			atomic64_inc(&zram->stats.failed_reads);
+			bio->bi_status = BLK_STS_IOERR;
+			break;
+		}
+		flush_dcache_page(bv.bv_page);
+
+		slot_lock(zram, index);
+		mark_slot_accessed(zram, index);
+		slot_unlock(zram, index);
+
+		bio_advance_iter_single(bio, &iter, bv.bv_len);
+	} while (iter.bi_size);
+
+	bio_end_io_acct(bio, start_time);
+	bio_endio(bio);
+}
+
+static void zram_bio_write(struct zram *zram, struct bio *bio)
+{
+	unsigned long start_time = bio_start_io_acct(bio);
+	struct bvec_iter iter = bio->bi_iter;
+
+	do {
+		unsigned long index = iter.bi_sector >> SECTORS_PER_PAGE_SHIFT;
+		u32 offset = (iter.bi_sector & (SECTORS_PER_PAGE - 1)) <<
+				SECTOR_SHIFT;
+		struct bio_vec bv = bio_iter_iovec(bio, iter);
+
+		bv.bv_len = min_t(u32, bv.bv_len, PAGE_SIZE - offset);
+
+		if (zram_bvec_write(zram, &bv, index, offset) < 0) {
+			atomic64_inc(&zram->stats.failed_writes);
+			bio->bi_status = BLK_STS_IOERR;
+			break;
+		}
+
+		slot_lock(zram, index);
+		mark_slot_accessed(zram, index);
+		slot_unlock(zram, index);
+
+		bio_advance_iter_single(bio, &iter, bv.bv_len);
+	} while (iter.bi_size);
+
+	bio_end_io_acct(bio, start_time);
+	bio_endio(bio);
+}
+
+/*
+ * Handler function for all zram I/O requests.
+ */
+static void zram_submit_bio(struct bio *bio)
+{
+	struct zram *zram = bio->bi_bdev->bd_disk->private_data;
+
+	switch (bio_op(bio)) {
+	case REQ_OP_READ:
+		zram_bio_read(zram, bio);
+		break;
+	case REQ_OP_WRITE:
+		zram_bio_write(zram, bio);
+		break;
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		zram_bio_discard(zram, bio);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		bio_endio(bio);
+	}
+}
+
+static void zram_slot_free_notify(struct block_device *bdev,
+				unsigned long index)
+{
+	struct zram *zram;
+
+	zram = bdev->bd_disk->private_data;
+
+	atomic64_inc(&zram->stats.notify_free);
+	if (!slot_trylock(zram, index)) {
+		atomic64_inc(&zram->stats.miss_free);
+		return;
+	}
+
+	slot_free(zram, index);
+	slot_unlock(zram, index);
+}
+
+static void zram_comp_params_reset(struct zram *zram)
+{
+	u32 prio;
+
+	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
+		comp_params_reset(zram, prio);
+	}
+}
+
+static void zram_destroy_comps(struct zram *zram)
+{
+	u32 prio;
+
+	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
+		struct zcomp *comp = zram->comps[prio];
+
+		zram->comps[prio] = NULL;
+		if (!comp)
+			continue;
+		zcomp_destroy(comp);
+	}
+
+	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++)
+		zram->comp_algs[prio] = NULL;
+
+	zram_comp_params_reset(zram);
+	comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
+}
+
+static void zram_reset_device(struct zram *zram)
+{
+	guard(rwsem_write)(&zram->dev_lock);
+
+	zram->limit_pages = 0;
+
+	set_capacity_and_notify(zram->disk, 0);
+	part_stat_set_all(zram->disk->part0, 0);
+
+	/* I/O operation under all of CPU are done so let's free */
+	zram_meta_free(zram, zram->disksize);
+	zram->disksize = 0;
+	zram_destroy_comps(zram);
+	memset(&zram->stats, 0, sizeof(zram->stats));
+	reset_bdev(zram);
+}
+
+static ssize_t disksize_store(struct device *dev, struct device_attribute *attr,
+			      const char *buf, size_t len)
+{
+	unsigned long num_pages;
+	u64 disksize;
+	struct zcomp *comp;
+	struct zram *zram = dev_to_zram(dev);
+	int err;
+	u32 prio;
+
+	disksize = memparse(buf, NULL);
+	if (!disksize)
+		return -EINVAL;
+
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram)) {
+		pr_info("Cannot change disksize for initialized device\n");
+		return -EBUSY;
+	}
+
+	disksize = PAGE_ALIGN(disksize);
+	num_pages = disksize >> PAGE_SHIFT;
+	/* Slots are addressed by an unsigned long index */
+	if (!num_pages || ((u64)num_pages << PAGE_SHIFT) != disksize)
+		return -EINVAL;
+
+	if (!zram_meta_alloc(zram, disksize))
+		return -ENOMEM;
+
+	for (prio = ZRAM_PRIMARY_COMP; prio < ZRAM_MAX_COMPS; prio++) {
+		if (!zram->comp_algs[prio])
+			continue;
+
+		comp = zcomp_create(zram->comp_algs[prio],
+				    &zram->params[prio]);
+		if (IS_ERR(comp)) {
+			pr_err("Cannot initialise %s compressing backend\n",
+			       zram->comp_algs[prio]);
+			err = PTR_ERR(comp);
+			goto out_free_comps;
+		}
+
+		zram->comps[prio] = comp;
+	}
+	zram->disksize = disksize;
+	set_capacity_and_notify(zram->disk, zram->disksize >> SECTOR_SHIFT);
+
+	return len;
+
+out_free_comps:
+	zram_destroy_comps(zram);
+	zram_meta_free(zram, disksize);
+	return err;
+}
+
+static ssize_t reset_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	int ret;
+	unsigned short do_reset;
+	struct zram *zram;
+	struct gendisk *disk;
+
+	ret = kstrtou16(buf, 10, &do_reset);
+	if (ret)
+		return ret;
+
+	if (!do_reset)
+		return -EINVAL;
+
+	zram = dev_to_zram(dev);
+	disk = zram->disk;
+
+	mutex_lock(&disk->open_mutex);
+	/* Do not reset an active device or claimed device */
+	if (disk_openers(disk) || zram->claim) {
+		mutex_unlock(&disk->open_mutex);
+		return -EBUSY;
+	}
+
+	/* From now on, anyone can't open /dev/zram[0-9] */
+	zram->claim = true;
+	mutex_unlock(&disk->open_mutex);
+
+	/* Make sure all the pending I/O are finished */
+	sync_blockdev(disk->part0);
+	zram_reset_device(zram);
+
+	mutex_lock(&disk->open_mutex);
+	zram->claim = false;
+	mutex_unlock(&disk->open_mutex);
+
+	return len;
+}
+
+static int zram_open(struct gendisk *disk, blk_mode_t mode)
+{
+	struct zram *zram = disk->private_data;
+
+	WARN_ON(!mutex_is_locked(&disk->open_mutex));
+
+	/* zram was claimed to reset so open request fails */
+	if (zram->claim)
+		return -EBUSY;
+	return 0;
+}
+
+static const struct block_device_operations zram_devops = {
+	.open = zram_open,
+	.submit_bio = zram_submit_bio,
+	.swap_slot_free_notify = zram_slot_free_notify,
+	.owner = THIS_MODULE
+};
+
+static DEVICE_ATTR_RO(io_stat);
+static DEVICE_ATTR_RO(mm_stat);
+static DEVICE_ATTR_RO(debug_stat);
+static DEVICE_ATTR_WO(compact);
+static DEVICE_ATTR_RW(disksize);
+static DEVICE_ATTR_RO(initstate);
+static DEVICE_ATTR_WO(reset);
+static DEVICE_ATTR_WO(mem_limit);
+static DEVICE_ATTR_WO(mem_used_max);
+static DEVICE_ATTR_WO(idle);
+static DEVICE_ATTR_RW(comp_algorithm);
+#ifdef CONFIG_ZRAM_WRITEBACK
+static DEVICE_ATTR_RO(bd_stat);
+static DEVICE_ATTR_RW(backing_dev);
+static DEVICE_ATTR_WO(writeback);
+static DEVICE_ATTR_RW(writeback_limit);
+static DEVICE_ATTR_RW(writeback_limit_enable);
+static DEVICE_ATTR_RW(writeback_batch_size);
+static DEVICE_ATTR_RW(compressed_writeback);
+#endif
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static DEVICE_ATTR_RW(recomp_algorithm);
+static DEVICE_ATTR_WO(recompress);
+#endif
+static DEVICE_ATTR_WO(algorithm_params);
+
+static struct attribute *zram_disk_attrs[] = {
+	&dev_attr_disksize.attr,
+	&dev_attr_initstate.attr,
+	&dev_attr_reset.attr,
+	&dev_attr_compact.attr,
+	&dev_attr_mem_limit.attr,
+	&dev_attr_mem_used_max.attr,
+	&dev_attr_idle.attr,
+	&dev_attr_comp_algorithm.attr,
+#ifdef CONFIG_ZRAM_WRITEBACK
+	&dev_attr_bd_stat.attr,
+	&dev_attr_backing_dev.attr,
+	&dev_attr_writeback.attr,
+	&dev_attr_writeback_limit.attr,
+	&dev_attr_writeback_limit_enable.attr,
+	&dev_attr_writeback_batch_size.attr,
+	&dev_attr_compressed_writeback.attr,
+#endif
+	&dev_attr_io_stat.attr,
+	&dev_attr_mm_stat.attr,
+	&dev_attr_debug_stat.attr,
+#ifdef CONFIG_ZRAM_MULTI_COMP
+	&dev_attr_recomp_algorithm.attr,
+	&dev_attr_recompress.attr,
+#endif
+	&dev_attr_algorithm_params.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(zram_disk);
+
+/*
+ * Allocate and initialize new zram device. the function returns
+ * '>= 0' device_id upon success, and negative value otherwise.
+ */
+static int zram_add(void)
+{
+	struct queue_limits lim = {
+		.logical_block_size		= ZRAM_LOGICAL_BLOCK_SIZE,
+		/*
+		 * To ensure that we always get PAGE_SIZE aligned and
+		 * n*PAGE_SIZED sized I/O requests.
+		 */
+		.physical_block_size		= PAGE_SIZE,
+		.io_min				= PAGE_SIZE,
+		.io_opt				= PAGE_SIZE,
+		.max_hw_discard_sectors		= UINT_MAX,
+		/*
+		 * zram_bio_discard() will clear all logical blocks if logical
+		 * block size is identical with physical block size(PAGE_SIZE).
+		 * But if it is different, we will skip discarding some parts of
+		 * logical blocks in the part of the request range which isn't
+		 * aligned to physical block size.  So we can't ensure that all
+		 * discarded logical blocks are zeroed.
+		 */
+#if ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE
+		.max_write_zeroes_sectors	= UINT_MAX,
+#endif
+		.features			= BLK_FEAT_STABLE_WRITES |
+						  BLK_FEAT_SYNCHRONOUS,
+	};
+	struct zram *zram;
+	int ret, device_id;
+
+	zram = kzalloc_obj(struct zram);
+	if (!zram)
+		return -ENOMEM;
+
+	ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
+	if (ret < 0)
+		goto out_free_dev;
+	device_id = ret;
+
+	init_rwsem(&zram->dev_lock);
+#ifdef CONFIG_ZRAM_WRITEBACK
+	zram->wb_batch_size = 32;
+	zram->compressed_wb = false;
+#endif
+
+	/* gendisk structure */
+	zram->disk = blk_alloc_disk(&lim, NUMA_NO_NODE);
+	if (IS_ERR(zram->disk)) {
+		pr_err("Error allocating disk structure for device %d\n",
+			device_id);
+		ret = PTR_ERR(zram->disk);
+		goto out_free_idr;
+	}
+
+	zram->disk->major = zram_major;
+	zram->disk->first_minor = device_id;
+	zram->disk->minors = 1;
+	zram->disk->flags |= GENHD_FL_NO_PART;
+	zram->disk->fops = &zram_devops;
+	zram->disk->private_data = zram;
+	snprintf(zram->disk->disk_name, 16, "zram%d", device_id);
+	zram_comp_params_reset(zram);
+	comp_algorithm_set(zram, ZRAM_PRIMARY_COMP, default_compressor);
+
+	/* Actual capacity set using sysfs (/sys/block/zram<id>/disksize */
+	set_capacity(zram->disk, 0);
+	ret = device_add_disk(NULL, zram->disk, zram_disk_groups);
+	if (ret)
+		goto out_cleanup_disk;
+
+	zram_debugfs_register(zram);
+	pr_info("Added device: %s\n", zram->disk->disk_name);
+	return device_id;
+
+out_cleanup_disk:
+	put_disk(zram->disk);
+out_free_idr:
+	idr_remove(&zram_index_idr, device_id);
+out_free_dev:
+	kfree(zram);
+	return ret;
+}
+
+static int zram_remove(struct zram *zram)
+{
+	bool claimed;
+
+	mutex_lock(&zram->disk->open_mutex);
+	if (disk_openers(zram->disk)) {
+		mutex_unlock(&zram->disk->open_mutex);
+		return -EBUSY;
+	}
+
+	claimed = zram->claim;
+	if (!claimed)
+		zram->claim = true;
+	mutex_unlock(&zram->disk->open_mutex);
+
+	zram_debugfs_unregister(zram);
+
+	if (claimed) {
+		/*
+		 * If we were claimed by reset_store(), del_gendisk() will
+		 * wait until reset_store() is done, so nothing need to do.
+		 */
+		;
+	} else {
+		/* Make sure all the pending I/O are finished */
+		sync_blockdev(zram->disk->part0);
+		zram_reset_device(zram);
+	}
+
+	pr_info("Removed device: %s\n", zram->disk->disk_name);
+
+	del_gendisk(zram->disk);
+
+	/* del_gendisk drains pending reset_store */
+	WARN_ON_ONCE(claimed && zram->claim);
+
+	/*
+	 * disksize_store() may be called in between zram_reset_device()
+	 * and del_gendisk(), so run the last reset to avoid leaking
+	 * anything allocated with disksize_store()
+	 */
+	zram_reset_device(zram);
+
+	put_disk(zram->disk);
+	kfree(zram);
+	return 0;
+}
+
+/* zram-control sysfs attributes */
+
+/*
+ * NOTE: hot_add attribute is not the usual read-only sysfs attribute. In a
+ * sense that reading from this file does alter the state of your system -- it
+ * creates a new un-initialized zram device and returns back this device's
+ * device_id (or an error code if it fails to create a new device).
+ */
+static ssize_t hot_add_show(const struct class *class,
+			const struct class_attribute *attr,
+			char *buf)
+{
+	int ret;
+
+	mutex_lock(&zram_index_mutex);
+	ret = zram_add();
+	mutex_unlock(&zram_index_mutex);
+
+	if (ret < 0)
+		return ret;
+	return sysfs_emit(buf, "%d\n", ret);
+}
+/* This attribute must be set to 0400, so CLASS_ATTR_RO() can not be used */
+static struct class_attribute class_attr_hot_add =
+	__ATTR(hot_add, 0400, hot_add_show, NULL);
+
+static ssize_t hot_remove_store(const struct class *class,
+			const struct class_attribute *attr,
+			const char *buf,
+			size_t count)
+{
+	struct zram *zram;
+	int ret, dev_id;
+
+	/* dev_id is gendisk->first_minor, which is `int' */
+	ret = kstrtoint(buf, 10, &dev_id);
+	if (ret)
+		return ret;
+	if (dev_id < 0)
+		return -EINVAL;
+
+	mutex_lock(&zram_index_mutex);
+
+	zram = idr_find(&zram_index_idr, dev_id);
+	if (zram) {
+		ret = zram_remove(zram);
+		if (!ret)
+			idr_remove(&zram_index_idr, dev_id);
+	} else {
+		ret = -ENODEV;
+	}
+
+	mutex_unlock(&zram_index_mutex);
+	return ret ? ret : count;
+}
+static CLASS_ATTR_WO(hot_remove);
+
+static struct attribute *zram_control_class_attrs[] = {
+	&class_attr_hot_add.attr,
+	&class_attr_hot_remove.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(zram_control_class);
+
+static struct class zram_control_class = {
+	.name		= "zram-control",
+	.class_groups	= zram_control_class_groups,
+};
+
+static int zram_remove_cb(int id, void *ptr, void *data)
+{
+	WARN_ON_ONCE(zram_remove(ptr));
+	return 0;
+}
+
+static void destroy_devices(void)
+{
+	class_unregister(&zram_control_class);
+	idr_for_each(&zram_index_idr, &zram_remove_cb, NULL);
+	zram_debugfs_destroy();
+	idr_destroy(&zram_index_idr);
+	unregister_blkdev(zram_major, "zram");
+	cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
+}
+
+static int __init zram_init(void)
+{
+	struct zram_table_entry zram_te;
+	int ret;
+
+	BUILD_BUG_ON(__NR_ZRAM_PAGEFLAGS > sizeof(zram_te.attr.flags) * 8);
+
+	ret = cpuhp_setup_state_multi(CPUHP_ZCOMP_PREPARE, "block/zram:prepare",
+				      zcomp_cpu_up_prepare, zcomp_cpu_dead);
+	if (ret < 0)
+		return ret;
+
+	ret = class_register(&zram_control_class);
+	if (ret) {
+		pr_err("Unable to register zram-control class\n");
+		cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
+		return ret;
+	}
+
+	zram_debugfs_create();
+	zram_major = register_blkdev(0, "zram");
+	if (zram_major <= 0) {
+		pr_err("Unable to get major number\n");
+		class_unregister(&zram_control_class);
+		cpuhp_remove_multi_state(CPUHP_ZCOMP_PREPARE);
+		return -EBUSY;
+	}
+
+	while (num_devices != 0) {
+		mutex_lock(&zram_index_mutex);
+		ret = zram_add();
+		mutex_unlock(&zram_index_mutex);
+		if (ret < 0)
+			goto out_error;
+		num_devices--;
+	}
+
+	return 0;
+
+out_error:
+	destroy_devices();
+	return ret;
+}
+
+static void __exit zram_exit(void)
+{
+	destroy_devices();
+}
+
+module_init(zram_init);
+module_exit(zram_exit);
+
+module_param(num_devices, uint, 0);
+MODULE_PARM_DESC(num_devices, "Number of pre-created zram devices");
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");
+MODULE_DESCRIPTION("Compressed RAM Block Device");
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
new file mode 100644
index 000000000..7a55d7514
--- /dev/null
+++ b/drivers/block/zram/zram_drv.h
@@ -0,0 +1,161 @@
+/*
+ * Compressed RAM block device
+ *
+ * Copyright (C) 2008, 2009, 2010  Nitin Gupta
+ *               2012, 2013 Minchan Kim
+ *
+ * This code is released using a dual license strategy: BSD/GPL
+ * You can choose the licence that better fits your requirements.
+ *
+ * Released under the terms of 3-clause BSD License
+ * Released under the terms of GNU General Public License Version 2.0
+ *
+ */
+
+#ifndef _ZRAM_DRV_H_
+#define _ZRAM_DRV_H_
+
+#include <asm/byteorder.h>
+#include <linux/rwsem.h>
+#include <linux/zsmalloc.h>
+
+#include "zcomp.h"
+
+#define SECTORS_PER_PAGE_SHIFT	(PAGE_SHIFT - SECTOR_SHIFT)
+#define SECTORS_PER_PAGE	(1 << SECTORS_PER_PAGE_SHIFT)
+#define ZRAM_LOGICAL_BLOCK_SHIFT 12
+#define ZRAM_LOGICAL_BLOCK_SIZE	(1 << ZRAM_LOGICAL_BLOCK_SHIFT)
+#define ZRAM_SECTOR_PER_LOGICAL_BLOCK	\
+	(1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT))
+
+/*
+ * ZRAM is mainly used for memory efficiency so we want to keep memory
+ * footprint small and thus squeeze size and zram pageflags into a flags
+ * member. The lower ZRAM_FLAG_SHIFT bits is for object size (excluding
+ * header), which cannot be larger than PAGE_SIZE (requiring PAGE_SHIFT
+ * bits), the higher bits are for zram_pageflags.
+ *
+ * We use BUILD_BUG_ON() to make sure that zram pageflags don't overflow.
+ */
+#define ZRAM_FLAG_SHIFT (PAGE_SHIFT + 1)
+
+/* Only 2 bits are allowed for comp priority index */
+#define ZRAM_COMP_PRIORITY_MASK	0x3
+
+/* Flags for zram pages (table[page_no].flags) */
+enum zram_pageflags {
+	ZRAM_SAME = ZRAM_FLAG_SHIFT,	/* Page consists the same element */
+	ZRAM_ENTRY_LOCK, /* entry access lock bit */
+	ZRAM_WB,	/* page is stored on backing_device */
+	ZRAM_PP_SLOT,	/* Selected for post-processing */
+	ZRAM_HUGE,	/* Incompressible page */
+	ZRAM_IDLE,	/* not accessed page since last idle marking */
+	ZRAM_INCOMPRESSIBLE, /* none of the algorithms could compress it */
+
+	ZRAM_COMP_PRIORITY_BIT1, /* First bit of comp priority index */
+	ZRAM_COMP_PRIORITY_BIT2, /* Second bit of comp priority index */
+
+	__NR_ZRAM_PAGEFLAGS,
+};
+
+/*
+ * The slot lock is a bit-wait lock on the whole __lock word, while
+ * flags and ac_time alias that word as two u32s.  The lock bit must
+ * land in the slot that ZRAM_ENTRY_LOCK reserves in attr.flags; on
+ * 64-bit big-endian the flags word maps to the upper half of __lock,
+ * so the bit position has to be shifted up.
+ */
+#if defined(CONFIG_64BIT) && defined(__BIG_ENDIAN)
+#define ZRAM_ENTRY_LOCK_BIT  (ZRAM_ENTRY_LOCK + 32)
+#else
+#define ZRAM_ENTRY_LOCK_BIT  ZRAM_ENTRY_LOCK
+#endif
+
+/*
+ * Allocated for each disk page.  We use bit-lock (ZRAM_ENTRY_LOCK bit
+ * of flags) to save memory.  There can be plenty of entries and standard
+ * locking primitives (e.g. mutex) will significantly increase sizeof()
+ * of each entry and hence of the meta table.
+ */
+struct zram_table_entry {
+	unsigned long handle;
+	union {
+		unsigned long __lock;
+		struct attr {
+			u32 flags;
+#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
+			u32 ac_time;
+#endif
+		} attr;
+	};
+};
+
+struct zram_stats {
+	atomic64_t compr_data_size;	/* compressed size of pages stored */
+	atomic64_t failed_reads;	/* can happen when memory is too low */
+	atomic64_t failed_writes;	/* can happen when memory is too low */
+	atomic64_t notify_free;	/* no. of swap slot free notifications */
+	atomic64_t same_pages;		/* no. of same element filled pages */
+	atomic64_t huge_pages;		/* no. of huge pages */
+	atomic64_t huge_pages_since;	/* no. of huge pages since zram set up */
+	atomic64_t pages_stored;	/* no. of pages currently stored */
+	atomic_long_t max_used_pages;	/* no. of maximum pages stored */
+	atomic64_t miss_free;		/* no. of missed free */
+#ifdef	CONFIG_ZRAM_WRITEBACK
+	atomic64_t bd_count;		/* no. of pages in backing device */
+	atomic64_t bd_reads;		/* no. of reads from backing device */
+	atomic64_t bd_writes;		/* no. of writes from backing device */
+#endif
+};
+
+#ifdef CONFIG_ZRAM_MULTI_COMP
+#define ZRAM_PRIMARY_COMP	0U
+#define ZRAM_SECONDARY_COMP	1U
+#define ZRAM_MAX_COMPS	4U
+#else
+#define ZRAM_PRIMARY_COMP	0U
+#define ZRAM_SECONDARY_COMP	0U
+#define ZRAM_MAX_COMPS	1U
+#endif
+
+struct zram {
+	struct zram_table_entry *table;
+	struct lockdep_map table_lock_map;
+	struct lock_class_key table_lock_key;
+	struct zs_pool *mem_pool;
+	struct zcomp *comps[ZRAM_MAX_COMPS];
+	struct zcomp_params params[ZRAM_MAX_COMPS];
+	struct gendisk *disk;
+	/* Locks the device either in exclusive or in shared mode */
+	struct rw_semaphore dev_lock;
+	/*
+	 * the number of pages zram can consume for storing compressed data
+	 */
+	unsigned long limit_pages;
+
+	struct zram_stats stats;
+	/*
+	 * This is the limit on amount of *uncompressed* worth of data
+	 * we can store in a disk.
+	 */
+	u64 disksize;	/* bytes */
+	const char *comp_algs[ZRAM_MAX_COMPS];
+	/*
+	 * zram is claimed so open request will be failed
+	 */
+	bool claim; /* Protected by disk->open_mutex */
+#ifdef CONFIG_ZRAM_WRITEBACK
+	struct file *backing_dev;
+	bool wb_limit_enable;
+	bool compressed_wb;
+	u32 wb_batch_size;
+	u64 bd_wb_limit;
+	struct block_device *bdev;
+	unsigned long *bitmap;
+	unsigned long nr_pages;
+#endif
+#ifdef CONFIG_ZRAM_MEMORY_TRACKING
+	struct dentry *debugfs_dir;
+#endif
+};
+#endif