coccinelle: alloc_cast: drop removed allocatorsgrafted

- pci_alloc_consistent() and pci_zalloc_consistent() were removed by
  commit 7968778914e5
  ("PCI: Remove the deprecated "pci-dma-compat.h" API")

- kmem_alloc() was removed by commit f078d4ea8276
  ("xfs: convert kmem_alloc() to kmalloc()")

- kmem_zalloc() was removed by commit 10634530f7ba
  ("xfs: convert kmem_zalloc() to kzalloc()")

- kmem_zone_alloc() and kmem_zone_zalloc() were removed by commit
  bae633a4a283 ("xfs: remove xfs_zone_{alloc,zalloc} helpers")

So drop them from the rules.

No functional change.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

1 files changed, 1832 insertions, 0 deletions

diff --git a/mm/zswap.c b/mm/zswap.c
new file mode 100644
index 000000000..761cd699e
--- /dev/null
+++ b/mm/zswap.c
@@ -0,0 +1,1832 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * zswap.c - zswap driver file
+ *
+ * zswap is a cache that takes pages that are in the process
+ * of being swapped out and attempts to compress and store them in a
+ * RAM-based memory pool.  This can result in a significant I/O reduction on
+ * the swap device and, in the case where decompressing from RAM is faster
+ * than reading from the swap device, can also improve workload performance.
+ *
+ * Copyright (C) 2012  Seth Jennings <sjenning@linux.vnet.ibm.com>
+*/
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/cpu.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/types.h>
+#include <linux/atomic.h>
+#include <linux/swap.h>
+#include <linux/crypto.h>
+#include <linux/scatterlist.h>
+#include <linux/mempolicy.h>
+#include <linux/mempool.h>
+#include <crypto/acompress.h>
+#include <crypto/scatterwalk.h>
+#include <linux/zswap.h>
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
+#include <linux/swapops.h>
+#include <linux/writeback.h>
+#include <linux/pagemap.h>
+#include <linux/workqueue.h>
+#include <linux/list_lru.h>
+#include <linux/zsmalloc.h>
+
+#include "swap.h"
+#include "internal.h"
+
+/*********************************
+* statistics
+**********************************/
+/* The number of pages currently stored in zswap */
+atomic_long_t zswap_stored_pages = ATOMIC_LONG_INIT(0);
+/* The number of incompressible pages currently stored in zswap */
+static atomic_long_t zswap_stored_incompressible_pages = ATOMIC_LONG_INIT(0);
+
+/*
+ * The statistics below are not protected from concurrent access for
+ * performance reasons so they may not be a 100% accurate.  However,
+ * they do provide useful information on roughly how many times a
+ * certain event is occurring.
+*/
+
+/* Pool limit was hit (see zswap_max_pool_percent) */
+static u64 zswap_pool_limit_hit;
+/* Pages written back when pool limit was reached */
+static u64 zswap_written_back_pages;
+/* Store failed due to a reclaim failure after pool limit was reached */
+static u64 zswap_reject_reclaim_fail;
+/* Store failed due to compression algorithm failure */
+static u64 zswap_reject_compress_fail;
+/* Compressed page was too big for the allocator to (optimally) store */
+static u64 zswap_reject_compress_poor;
+/* Load or writeback failed due to decompression failure */
+static u64 zswap_decompress_fail;
+/* Store failed because underlying allocator could not get memory */
+static u64 zswap_reject_alloc_fail;
+/* Store failed because the entry metadata could not be allocated (rare) */
+static u64 zswap_reject_kmemcache_fail;
+
+/* Shrinker work queue */
+static struct workqueue_struct *shrink_wq;
+/* Pool limit was hit, we need to calm down */
+static bool zswap_pool_reached_full;
+
+/*********************************
+* tunables
+**********************************/
+
+#define ZSWAP_PARAM_UNSET ""
+
+static int zswap_setup(void);
+
+/* Enable/disable zswap */
+static DEFINE_STATIC_KEY_MAYBE(CONFIG_ZSWAP_DEFAULT_ON, zswap_ever_enabled);
+static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON);
+static int zswap_enabled_param_set(const char *,
+				   const struct kernel_param *);
+static const struct kernel_param_ops zswap_enabled_param_ops = {
+	.set =		zswap_enabled_param_set,
+	.get =		param_get_bool,
+};
+module_param_cb(enabled, &zswap_enabled_param_ops, &zswap_enabled, 0644);
+
+/* Crypto compressor to use */
+static char *zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
+static int zswap_compressor_param_set(const char *,
+				      const struct kernel_param *);
+static const struct kernel_param_ops zswap_compressor_param_ops = {
+	.set =		zswap_compressor_param_set,
+	.get =		param_get_charp,
+	.free =		param_free_charp,
+};
+module_param_cb(compressor, &zswap_compressor_param_ops,
+		&zswap_compressor, 0644);
+
+/* The maximum percentage of memory that the compressed pool can occupy */
+static unsigned int zswap_max_pool_percent = 20;
+module_param_named(max_pool_percent, zswap_max_pool_percent, uint, 0644);
+
+/* The threshold for accepting new pages after the max_pool_percent was hit */
+static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */
+module_param_named(accept_threshold_percent, zswap_accept_thr_percent,
+		   uint, 0644);
+
+/* Enable/disable memory pressure-based shrinker. */
+static bool zswap_shrinker_enabled = IS_ENABLED(
+		CONFIG_ZSWAP_SHRINKER_DEFAULT_ON);
+module_param_named(shrinker_enabled, zswap_shrinker_enabled, bool, 0644);
+
+bool zswap_is_enabled(void)
+{
+	return zswap_enabled;
+}
+
+bool zswap_never_enabled(void)
+{
+	return !static_branch_maybe(CONFIG_ZSWAP_DEFAULT_ON, &zswap_ever_enabled);
+}
+
+/*********************************
+* data structures
+**********************************/
+
+struct crypto_acomp_ctx {
+	struct crypto_acomp *acomp;
+	struct acomp_req *req;
+	struct crypto_wait wait;
+	u8 *buffer;
+	struct mutex mutex;
+};
+
+/*
+ * The lock ordering is zswap_tree.lock -> zswap_pool.lru_lock.
+ * The only case where lru_lock is not acquired while holding tree.lock is
+ * when a zswap_entry is taken off the lru for writeback, in that case it
+ * needs to be verified that it's still valid in the tree.
+ */
+struct zswap_pool {
+	struct zs_pool *zs_pool;
+	struct crypto_acomp_ctx __percpu *acomp_ctx;
+	struct percpu_ref ref;
+	struct list_head list;
+	struct work_struct release_work;
+	struct hlist_node node;
+	char tfm_name[CRYPTO_MAX_ALG_NAME];
+};
+
+/* Global LRU lists shared by all zswap pools. */
+static struct list_lru zswap_list_lru;
+
+/* The lock protects zswap_next_shrink updates. */
+static DEFINE_SPINLOCK(zswap_shrink_lock);
+static struct mem_cgroup *zswap_next_shrink;
+static struct work_struct zswap_shrink_work;
+static struct shrinker *zswap_shrinker;
+
+/*
+ * struct zswap_entry
+ *
+ * This structure contains the metadata for tracking a single compressed
+ * page within zswap.
+ *
+ * swpentry - associated swap entry, the offset indexes into the xarray
+ * length - the length in bytes of the compressed page data.  Needed during
+ *          decompression.
+ * referenced - true if the entry recently entered the zswap pool. Unset by the
+ *              writeback logic. The entry is only reclaimed by the writeback
+ *              logic if referenced is unset. See comments in the shrinker
+ *              section for context.
+ * pool - the zswap_pool the entry's data is in
+ * handle - zsmalloc allocation handle that stores the compressed page data
+ * objcg - the obj_cgroup that the compressed memory is charged to
+ * lru - handle to the pool's lru used to evict pages.
+ */
+struct zswap_entry {
+	swp_entry_t swpentry;
+	unsigned int length;
+	bool referenced;
+	struct zswap_pool *pool;
+	unsigned long handle;
+	struct obj_cgroup *objcg;
+	struct list_head lru;
+};
+
+static struct xarray *zswap_trees[MAX_SWAPFILES];
+static unsigned int nr_zswap_trees[MAX_SWAPFILES];
+
+/* RCU-protected iteration */
+static LIST_HEAD(zswap_pools);
+/* protects zswap_pools list modification */
+static DEFINE_SPINLOCK(zswap_pools_lock);
+/* pool counter to provide unique names to zsmalloc */
+static atomic_t zswap_pools_count = ATOMIC_INIT(0);
+
+enum zswap_init_type {
+	ZSWAP_UNINIT,
+	ZSWAP_INIT_SUCCEED,
+	ZSWAP_INIT_FAILED
+};
+
+static enum zswap_init_type zswap_init_state;
+
+/* used to ensure the integrity of initialization */
+static DEFINE_MUTEX(zswap_init_lock);
+
+/* init completed, but couldn't create the initial pool */
+static bool zswap_has_pool;
+
+/*********************************
+* helpers and fwd declarations
+**********************************/
+
+/* One swap address space for each 64M swap space */
+#define ZSWAP_ADDRESS_SPACE_SHIFT 14
+#define ZSWAP_ADDRESS_SPACE_PAGES (1 << ZSWAP_ADDRESS_SPACE_SHIFT)
+static inline struct xarray *swap_zswap_tree(swp_entry_t swp)
+{
+	return &zswap_trees[swp_type(swp)][swp_offset(swp)
+		>> ZSWAP_ADDRESS_SPACE_SHIFT];
+}
+
+#define zswap_pool_debug(msg, p)			\
+	pr_debug("%s pool %s\n", msg, (p)->tfm_name)
+
+/*********************************
+* pool functions
+**********************************/
+static void __zswap_pool_empty(struct percpu_ref *ref);
+
+static void acomp_ctx_free(struct crypto_acomp_ctx *acomp_ctx)
+{
+	if (!acomp_ctx)
+		return;
+
+	/*
+	 * If there was an error in allocating @acomp_ctx->req, it
+	 * would be set to NULL.
+	 */
+	if (acomp_ctx->req)
+		acomp_request_free(acomp_ctx->req);
+
+	acomp_ctx->req = NULL;
+
+	/*
+	 * We have to handle both cases here: an error pointer return from
+	 * crypto_alloc_acomp_node(); and a) NULL initialization by zswap, or
+	 * b) NULL assignment done in a previous call to acomp_ctx_free().
+	 */
+	if (!IS_ERR_OR_NULL(acomp_ctx->acomp))
+		crypto_free_acomp(acomp_ctx->acomp);
+
+	acomp_ctx->acomp = NULL;
+
+	kfree(acomp_ctx->buffer);
+	acomp_ctx->buffer = NULL;
+}
+
+static struct zswap_pool *zswap_pool_create(char *compressor)
+{
+	struct zswap_pool *pool;
+	char name[38]; /* 'zswap' + 32 char (max) num + \0 */
+	int ret, cpu;
+
+	if (!zswap_has_pool && !strcmp(compressor, ZSWAP_PARAM_UNSET))
+		return NULL;
+
+	pool = kzalloc_obj(*pool);
+	if (!pool)
+		return NULL;
+
+	/* unique name for each pool specifically required by zsmalloc */
+	snprintf(name, 38, "zswap%x", atomic_inc_return(&zswap_pools_count));
+	pool->zs_pool = zs_create_pool(name);
+	if (!pool->zs_pool)
+		goto error;
+
+	strscpy(pool->tfm_name, compressor, sizeof(pool->tfm_name));
+
+	/* Many things rely on the zero-initialization. */
+	pool->acomp_ctx = alloc_percpu_gfp(*pool->acomp_ctx,
+					   GFP_KERNEL | __GFP_ZERO);
+	if (!pool->acomp_ctx) {
+		pr_err("percpu alloc failed\n");
+		goto error;
+	}
+
+	/*
+	 * This is serialized against CPU hotplug operations. Hence, cores
+	 * cannot be offlined until this finishes.
+	 */
+	ret = cpuhp_state_add_instance(CPUHP_MM_ZSWP_POOL_PREPARE,
+				       &pool->node);
+
+	/*
+	 * cpuhp_state_add_instance() will not cleanup on failure since
+	 * we don't register a hotunplug callback.
+	 */
+	if (ret)
+		goto cpuhp_add_fail;
+
+	/* being the current pool takes 1 ref; this func expects the
+	 * caller to always add the new pool as the current pool
+	 */
+	ret = percpu_ref_init(&pool->ref, __zswap_pool_empty,
+			      PERCPU_REF_ALLOW_REINIT, GFP_KERNEL);
+	if (ret)
+		goto ref_fail;
+	INIT_LIST_HEAD(&pool->list);
+
+	zswap_pool_debug("created", pool);
+
+	return pool;
+
+ref_fail:
+	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
+
+cpuhp_add_fail:
+	for_each_possible_cpu(cpu)
+		acomp_ctx_free(per_cpu_ptr(pool->acomp_ctx, cpu));
+error:
+	if (pool->acomp_ctx)
+		free_percpu(pool->acomp_ctx);
+	if (pool->zs_pool)
+		zs_destroy_pool(pool->zs_pool);
+	kfree(pool);
+	return NULL;
+}
+
+static struct zswap_pool *__zswap_pool_create_fallback(void)
+{
+	if (!crypto_has_acomp(zswap_compressor, 0, 0) &&
+	    strcmp(zswap_compressor, CONFIG_ZSWAP_COMPRESSOR_DEFAULT)) {
+		pr_err("compressor %s not available, using default %s\n",
+		       zswap_compressor, CONFIG_ZSWAP_COMPRESSOR_DEFAULT);
+		param_free_charp(&zswap_compressor);
+		zswap_compressor = CONFIG_ZSWAP_COMPRESSOR_DEFAULT;
+	}
+
+	/* Default compressor should be available. Kconfig bug? */
+	if (WARN_ON_ONCE(!crypto_has_acomp(zswap_compressor, 0, 0))) {
+		zswap_compressor = ZSWAP_PARAM_UNSET;
+		return NULL;
+	}
+
+	return zswap_pool_create(zswap_compressor);
+}
+
+static void zswap_pool_destroy(struct zswap_pool *pool)
+{
+	int cpu;
+
+	zswap_pool_debug("destroying", pool);
+
+	cpuhp_state_remove_instance(CPUHP_MM_ZSWP_POOL_PREPARE, &pool->node);
+
+	for_each_possible_cpu(cpu)
+		acomp_ctx_free(per_cpu_ptr(pool->acomp_ctx, cpu));
+
+	free_percpu(pool->acomp_ctx);
+
+	zs_destroy_pool(pool->zs_pool);
+	kfree(pool);
+}
+
+static void __zswap_pool_release(struct work_struct *work)
+{
+	struct zswap_pool *pool = container_of(work, typeof(*pool),
+						release_work);
+
+	synchronize_rcu();
+
+	/* nobody should have been able to get a ref... */
+	WARN_ON(!percpu_ref_is_zero(&pool->ref));
+	percpu_ref_exit(&pool->ref);
+
+	/* pool is now off zswap_pools list and has no references. */
+	zswap_pool_destroy(pool);
+}
+
+static struct zswap_pool *zswap_pool_current(void);
+
+static void __zswap_pool_empty(struct percpu_ref *ref)
+{
+	struct zswap_pool *pool;
+
+	pool = container_of(ref, typeof(*pool), ref);
+
+	spin_lock_bh(&zswap_pools_lock);
+
+	WARN_ON(pool == zswap_pool_current());
+
+	list_del_rcu(&pool->list);
+
+	INIT_WORK(&pool->release_work, __zswap_pool_release);
+	schedule_work(&pool->release_work);
+
+	spin_unlock_bh(&zswap_pools_lock);
+}
+
+static int __must_check zswap_pool_tryget(struct zswap_pool *pool)
+{
+	if (!pool)
+		return 0;
+
+	return percpu_ref_tryget(&pool->ref);
+}
+
+/* The caller must already have a reference. */
+static void zswap_pool_get(struct zswap_pool *pool)
+{
+	percpu_ref_get(&pool->ref);
+}
+
+static void zswap_pool_put(struct zswap_pool *pool)
+{
+	percpu_ref_put(&pool->ref);
+}
+
+static struct zswap_pool *__zswap_pool_current(void)
+{
+	struct zswap_pool *pool;
+
+	pool = list_first_or_null_rcu(&zswap_pools, typeof(*pool), list);
+	WARN_ONCE(!pool && zswap_has_pool,
+		  "%s: no page storage pool!\n", __func__);
+
+	return pool;
+}
+
+static struct zswap_pool *zswap_pool_current(void)
+{
+	assert_spin_locked(&zswap_pools_lock);
+
+	return __zswap_pool_current();
+}
+
+static struct zswap_pool *zswap_pool_current_get(void)
+{
+	struct zswap_pool *pool;
+
+	rcu_read_lock();
+
+	pool = __zswap_pool_current();
+	if (!zswap_pool_tryget(pool))
+		pool = NULL;
+
+	rcu_read_unlock();
+
+	return pool;
+}
+
+/* type and compressor must be null-terminated */
+static struct zswap_pool *zswap_pool_find_get(char *compressor)
+{
+	struct zswap_pool *pool;
+
+	assert_spin_locked(&zswap_pools_lock);
+
+	list_for_each_entry_rcu(pool, &zswap_pools, list) {
+		if (strcmp(pool->tfm_name, compressor))
+			continue;
+		/* if we can't get it, it's about to be destroyed */
+		if (!zswap_pool_tryget(pool))
+			continue;
+		return pool;
+	}
+
+	return NULL;
+}
+
+static unsigned long zswap_max_pages(void)
+{
+	return totalram_pages() * zswap_max_pool_percent / 100;
+}
+
+static unsigned long zswap_accept_thr_pages(void)
+{
+	return zswap_max_pages() * zswap_accept_thr_percent / 100;
+}
+
+unsigned long zswap_total_pages(void)
+{
+	struct zswap_pool *pool;
+	unsigned long total = 0;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(pool, &zswap_pools, list)
+		total += zs_get_total_pages(pool->zs_pool);
+	rcu_read_unlock();
+
+	return total;
+}
+
+static bool zswap_check_limits(void)
+{
+	unsigned long cur_pages = zswap_total_pages();
+	unsigned long max_pages = zswap_max_pages();
+
+	if (cur_pages >= max_pages) {
+		zswap_pool_limit_hit++;
+		zswap_pool_reached_full = true;
+	} else if (zswap_pool_reached_full &&
+		   cur_pages <= zswap_accept_thr_pages()) {
+			zswap_pool_reached_full = false;
+	}
+	return zswap_pool_reached_full;
+}
+
+/*********************************
+* param callbacks
+**********************************/
+
+static int zswap_compressor_param_set(const char *val, const struct kernel_param *kp)
+{
+	struct zswap_pool *pool, *put_pool = NULL;
+	char *s = strstrip((char *)val);
+	bool create_pool = false;
+	int ret = 0;
+
+	mutex_lock(&zswap_init_lock);
+	switch (zswap_init_state) {
+	case ZSWAP_UNINIT:
+		/* Handled in zswap_setup() */
+		ret = param_set_charp(s, kp);
+		break;
+	case ZSWAP_INIT_SUCCEED:
+		if (!zswap_has_pool || strcmp(s, *(char **)kp->arg))
+			create_pool = true;
+		break;
+	case ZSWAP_INIT_FAILED:
+		pr_err("can't set param, initialization failed\n");
+		ret = -ENODEV;
+	}
+	mutex_unlock(&zswap_init_lock);
+
+	if (!create_pool)
+		return ret;
+
+	if (!crypto_has_acomp(s, 0, 0)) {
+		pr_err("compressor %s not available\n", s);
+		return -ENOENT;
+	}
+
+	spin_lock_bh(&zswap_pools_lock);
+
+	pool = zswap_pool_find_get(s);
+	if (pool) {
+		zswap_pool_debug("using existing", pool);
+		WARN_ON(pool == zswap_pool_current());
+		list_del_rcu(&pool->list);
+	}
+
+	spin_unlock_bh(&zswap_pools_lock);
+
+	if (!pool)
+		pool = zswap_pool_create(s);
+	else {
+		/*
+		 * Restore the initial ref dropped by percpu_ref_kill()
+		 * when the pool was decommissioned and switch it again
+		 * to percpu mode.
+		 */
+		percpu_ref_resurrect(&pool->ref);
+
+		/* Drop the ref from zswap_pool_find_get(). */
+		zswap_pool_put(pool);
+	}
+
+	if (pool)
+		ret = param_set_charp(s, kp);
+	else
+		ret = -EINVAL;
+
+	spin_lock_bh(&zswap_pools_lock);
+
+	if (!ret) {
+		put_pool = zswap_pool_current();
+		list_add_rcu(&pool->list, &zswap_pools);
+		zswap_has_pool = true;
+	} else if (pool) {
+		/*
+		 * Add the possibly pre-existing pool to the end of the pools
+		 * list; if it's new (and empty) then it'll be removed and
+		 * destroyed by the put after we drop the lock
+		 */
+		list_add_tail_rcu(&pool->list, &zswap_pools);
+		put_pool = pool;
+	}
+
+	spin_unlock_bh(&zswap_pools_lock);
+
+	/*
+	 * Drop the ref from either the old current pool,
+	 * or the new pool we failed to add
+	 */
+	if (put_pool)
+		percpu_ref_kill(&put_pool->ref);
+
+	return ret;
+}
+
+static int zswap_enabled_param_set(const char *val,
+				   const struct kernel_param *kp)
+{
+	int ret = -ENODEV;
+
+	/* if this is load-time (pre-init) param setting, only set param. */
+	if (system_state != SYSTEM_RUNNING)
+		return param_set_bool(val, kp);
+
+	mutex_lock(&zswap_init_lock);
+	switch (zswap_init_state) {
+	case ZSWAP_UNINIT:
+		if (zswap_setup())
+			break;
+		fallthrough;
+	case ZSWAP_INIT_SUCCEED:
+		if (!zswap_has_pool)
+			pr_err("can't enable, no pool configured\n");
+		else
+			ret = param_set_bool(val, kp);
+		break;
+	case ZSWAP_INIT_FAILED:
+		pr_err("can't enable, initialization failed\n");
+	}
+	mutex_unlock(&zswap_init_lock);
+
+	return ret;
+}
+
+/*********************************
+* lru functions
+**********************************/
+
+/* should be called under RCU */
+#ifdef CONFIG_MEMCG
+static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
+{
+	return entry->objcg ? obj_cgroup_memcg(entry->objcg) : NULL;
+}
+#else
+static inline struct mem_cgroup *mem_cgroup_from_entry(struct zswap_entry *entry)
+{
+	return NULL;
+}
+#endif
+
+static inline int entry_to_nid(struct zswap_entry *entry)
+{
+	return page_to_nid(virt_to_page(entry));
+}
+
+static void zswap_lru_add(struct list_lru *list_lru, struct zswap_entry *entry)
+{
+	int nid = entry_to_nid(entry);
+	struct mem_cgroup *memcg;
+
+	/*
+	 * Note that it is safe to use rcu_read_lock() here, even in the face of
+	 * concurrent memcg offlining:
+	 *
+	 * 1. list_lru_add() is called before list_lru_one is dead. The
+	 *    new entry will be reparented to memcg's parent's list_lru.
+	 * 2. list_lru_add() is called after list_lru_one is dead. The
+	 *    new entry will be added directly to memcg's parent's list_lru.
+	 *
+	 * Similar reasoning holds for list_lru_del().
+	 */
+	rcu_read_lock();
+	memcg = mem_cgroup_from_entry(entry);
+	/* will always succeed */
+	list_lru_add(list_lru, &entry->lru, nid, memcg);
+	rcu_read_unlock();
+}
+
+static void zswap_lru_del(struct list_lru *list_lru, struct zswap_entry *entry)
+{
+	int nid = entry_to_nid(entry);
+	struct mem_cgroup *memcg;
+
+	rcu_read_lock();
+	memcg = mem_cgroup_from_entry(entry);
+	/* will always succeed */
+	list_lru_del(list_lru, &entry->lru, nid, memcg);
+	rcu_read_unlock();
+}
+
+void zswap_lruvec_state_init(struct lruvec *lruvec)
+{
+	atomic_long_set(&lruvec->zswap_lruvec_state.nr_disk_swapins, 0);
+}
+
+void zswap_folio_swapin(struct folio *folio)
+{
+	struct lruvec *lruvec;
+
+	if (folio) {
+		rcu_read_lock();
+		lruvec = folio_lruvec(folio);
+		atomic_long_inc(&lruvec->zswap_lruvec_state.nr_disk_swapins);
+		rcu_read_unlock();
+	}
+}
+
+/*
+ * This function should be called when a memcg is being offlined.
+ *
+ * Since the global shrinker shrink_worker() may hold a reference
+ * of the memcg, we must check and release the reference in
+ * zswap_next_shrink.
+ *
+ * shrink_worker() must handle the case where this function releases
+ * the reference of memcg being shrunk.
+ */
+void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg)
+{
+	/* lock out zswap shrinker walking memcg tree */
+	spin_lock(&zswap_shrink_lock);
+	if (zswap_next_shrink == memcg) {
+		do {
+			zswap_next_shrink = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
+		} while (zswap_next_shrink && !mem_cgroup_online(zswap_next_shrink));
+	}
+	spin_unlock(&zswap_shrink_lock);
+}
+
+/*********************************
+* zswap entry functions
+**********************************/
+static struct kmem_cache *zswap_entry_cache;
+
+static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp, int nid)
+{
+	struct zswap_entry *entry;
+	entry = kmem_cache_alloc_node(zswap_entry_cache, gfp, nid);
+	if (!entry)
+		return NULL;
+	return entry;
+}
+
+static void zswap_entry_cache_free(struct zswap_entry *entry)
+{
+	kmem_cache_free(zswap_entry_cache, entry);
+}
+
+/*
+ * Carries out the common pattern of freeing an entry's zsmalloc allocation,
+ * freeing the entry itself, and decrementing the number of stored pages.
+ */
+static void zswap_entry_free(struct zswap_entry *entry)
+{
+	zswap_lru_del(&zswap_list_lru, entry);
+	zs_free(entry->pool->zs_pool, entry->handle);
+	zswap_pool_put(entry->pool);
+	if (entry->objcg) {
+		obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
+		obj_cgroup_put(entry->objcg);
+	}
+	if (entry->length == PAGE_SIZE)
+		atomic_long_dec(&zswap_stored_incompressible_pages);
+	zswap_entry_cache_free(entry);
+	atomic_long_dec(&zswap_stored_pages);
+}
+
+/*********************************
+* compressed storage functions
+**********************************/
+static int zswap_cpu_comp_prepare(unsigned int cpu, struct hlist_node *node)
+{
+	struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node);
+	struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu);
+	int ret = -ENOMEM;
+
+	/*
+	 * To handle cases where the CPU goes through online-offline-online
+	 * transitions, we return if the acomp_ctx has already been initialized.
+	 */
+	if (acomp_ctx->acomp) {
+		WARN_ON_ONCE(IS_ERR(acomp_ctx->acomp));
+		return 0;
+	}
+
+	acomp_ctx->buffer = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu));
+	if (!acomp_ctx->buffer)
+		return ret;
+
+	/*
+	 * In case of an error, crypto_alloc_acomp_node() returns an
+	 * error pointer, never NULL.
+	 */
+	acomp_ctx->acomp = crypto_alloc_acomp_node(pool->tfm_name, 0, 0, cpu_to_node(cpu));
+	if (IS_ERR(acomp_ctx->acomp)) {
+		pr_err("could not alloc crypto acomp %s : %pe\n",
+				pool->tfm_name, acomp_ctx->acomp);
+		ret = PTR_ERR(acomp_ctx->acomp);
+		goto fail;
+	}
+
+	/* acomp_request_alloc() returns NULL in case of an error. */
+	acomp_ctx->req = acomp_request_alloc(acomp_ctx->acomp);
+	if (!acomp_ctx->req) {
+		pr_err("could not alloc crypto acomp_request %s\n",
+		       pool->tfm_name);
+		goto fail;
+	}
+
+	crypto_init_wait(&acomp_ctx->wait);
+
+	/*
+	 * if the backend of acomp is async zip, crypto_req_done() will wakeup
+	 * crypto_wait_req(); if the backend of acomp is scomp, the callback
+	 * won't be called, crypto_wait_req() will return without blocking.
+	 */
+	acomp_request_set_callback(acomp_ctx->req, CRYPTO_TFM_REQ_MAY_BACKLOG,
+				   crypto_req_done, &acomp_ctx->wait);
+
+	mutex_init(&acomp_ctx->mutex);
+	return 0;
+
+fail:
+	acomp_ctx_free(acomp_ctx);
+	return ret;
+}
+
+static bool zswap_compress(struct page *page, struct zswap_entry *entry,
+			   struct zswap_pool *pool)
+{
+	struct crypto_acomp_ctx *acomp_ctx;
+	struct scatterlist input, output;
+	int comp_ret = 0, alloc_ret = 0;
+	unsigned int dlen = PAGE_SIZE;
+	unsigned long handle;
+	gfp_t gfp;
+	u8 *dst;
+	bool mapped = false;
+
+	acomp_ctx = raw_cpu_ptr(pool->acomp_ctx);
+	mutex_lock(&acomp_ctx->mutex);
+
+	dst = acomp_ctx->buffer;
+	sg_init_table(&input, 1);
+	sg_set_page(&input, page, PAGE_SIZE, 0);
+
+	sg_init_one(&output, dst, PAGE_SIZE);
+	acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen);
+
+	/*
+	 * it maybe looks a little bit silly that we send an asynchronous request,
+	 * then wait for its completion synchronously. This makes the process look
+	 * synchronous in fact.
+	 * Theoretically, acomp supports users send multiple acomp requests in one
+	 * acomp instance, then get those requests done simultaneously. but in this
+	 * case, zswap actually does store and load page by page, there is no
+	 * existing method to send the second page before the first page is done
+	 * in one thread doing zswap.
+	 * but in different threads running on different cpu, we have different
+	 * acomp instance, so multiple threads can do (de)compression in parallel.
+	 */
+	comp_ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
+	dlen = acomp_ctx->req->dlen;
+
+	/*
+	 * If a page cannot be compressed into a size smaller than PAGE_SIZE,
+	 * save the content as is without a compression, to keep the LRU order
+	 * of writebacks.  If writeback is disabled, reject the page since it
+	 * only adds metadata overhead.  swap_writeout() will put the page back
+	 * to the active LRU list in the case.
+	 */
+	if (comp_ret || !dlen || dlen >= PAGE_SIZE) {
+		rcu_read_lock();
+		if (!mem_cgroup_zswap_writeback_enabled(
+					folio_memcg(page_folio(page)))) {
+			rcu_read_unlock();
+			comp_ret = comp_ret ? comp_ret : -EINVAL;
+			goto unlock;
+		}
+		rcu_read_unlock();
+		comp_ret = 0;
+		dlen = PAGE_SIZE;
+		dst = kmap_local_page(page);
+		mapped = true;
+	}
+
+	gfp = GFP_NOWAIT | __GFP_NORETRY | __GFP_HIGHMEM | __GFP_MOVABLE;
+	handle = zs_malloc(pool->zs_pool, dlen, gfp, page_to_nid(page));
+	if (IS_ERR_VALUE(handle)) {
+		alloc_ret = PTR_ERR((void *)handle);
+		goto unlock;
+	}
+
+	zs_obj_write(pool->zs_pool, handle, dst, dlen);
+	entry->handle = handle;
+	entry->length = dlen;
+
+unlock:
+	if (mapped)
+		kunmap_local(dst);
+	if (comp_ret == -ENOSPC || alloc_ret == -ENOSPC)
+		zswap_reject_compress_poor++;
+	else if (comp_ret)
+		zswap_reject_compress_fail++;
+	else if (alloc_ret)
+		zswap_reject_alloc_fail++;
+
+	mutex_unlock(&acomp_ctx->mutex);
+	return comp_ret == 0 && alloc_ret == 0;
+}
+
+static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio)
+{
+	struct zswap_pool *pool = entry->pool;
+	struct scatterlist input[2]; /* zsmalloc returns an SG list 1-2 entries */
+	struct scatterlist output;
+	struct crypto_acomp_ctx *acomp_ctx;
+	int ret = 0, dlen;
+
+	acomp_ctx = raw_cpu_ptr(pool->acomp_ctx);
+	mutex_lock(&acomp_ctx->mutex);
+	zs_obj_read_sg_begin(pool->zs_pool, entry->handle, input, entry->length);
+
+	/* zswap entries of length PAGE_SIZE are not compressed. */
+	if (entry->length == PAGE_SIZE) {
+		void *dst;
+
+		WARN_ON_ONCE(input->length != PAGE_SIZE);
+
+		dst = kmap_local_folio(folio, 0);
+		memcpy_from_sglist(dst, input, 0, PAGE_SIZE);
+		dlen = PAGE_SIZE;
+		kunmap_local(dst);
+		flush_dcache_folio(folio);
+	} else {
+		sg_init_table(&output, 1);
+		sg_set_folio(&output, folio, PAGE_SIZE, 0);
+		acomp_request_set_params(acomp_ctx->req, input, &output,
+					 entry->length, PAGE_SIZE);
+		ret = crypto_acomp_decompress(acomp_ctx->req);
+		ret = crypto_wait_req(ret, &acomp_ctx->wait);
+		dlen = acomp_ctx->req->dlen;
+	}
+
+	zs_obj_read_sg_end(pool->zs_pool, entry->handle);
+	mutex_unlock(&acomp_ctx->mutex);
+
+	if (!ret && dlen == PAGE_SIZE)
+		return true;
+
+	zswap_decompress_fail++;
+	pr_alert_ratelimited("Decompression error from zswap (%d:%lu %s %u->%d)\n",
+						swp_type(entry->swpentry),
+						swp_offset(entry->swpentry),
+						entry->pool->tfm_name,
+						entry->length, dlen);
+	return false;
+}
+
+/*********************************
+* writeback code
+**********************************/
+/*
+ * Attempts to free an entry by adding a folio to the swap cache,
+ * decompressing the entry data into the folio, and issuing a
+ * bio write to write the folio back to the swap device.
+ *
+ * This can be thought of as a "resumed writeback" of the folio
+ * to the swap device.  We are basically resuming the same swap
+ * writeback path that was intercepted with the zswap_store()
+ * in the first place.  After the folio has been decompressed into
+ * the swap cache, the compressed version stored by zswap can be
+ * freed.
+ */
+static int zswap_writeback_entry(struct zswap_entry *entry,
+				 swp_entry_t swpentry)
+{
+	struct xarray *tree;
+	pgoff_t offset = swp_offset(swpentry);
+	struct folio *folio;
+	struct mempolicy *mpol;
+	struct swap_info_struct *si;
+	int ret = 0;
+
+	/* try to allocate swap cache folio */
+	si = get_swap_device(swpentry);
+	if (!si)
+		return -EEXIST;
+
+	mpol = get_task_policy(current);
+	folio = swap_cache_alloc_folio(swpentry, GFP_KERNEL, BIT(0), NULL, mpol,
+				       NO_INTERLEAVE_INDEX);
+	put_swap_device(si);
+
+	/*
+	 * Swap cache allocation might fail due to OOM, or the entry
+	 * may already be cached due to concurrent swapin or have been
+	 * freed. If already cached, a concurrent swapin made the folio
+	 * hot, so skip it. For the unlikely concurrent shrinker case,
+	 * it will be unlinked and freed when invalidated anyway.
+	 */
+	if (IS_ERR(folio))
+		return PTR_ERR(folio);
+
+	/*
+	 * folio is locked, and the swapcache is now secured against
+	 * concurrent swapping to and from the slot, and concurrent
+	 * swapoff so we can safely dereference the zswap tree here.
+	 * Verify that the swap entry hasn't been invalidated and recycled
+	 * behind our backs, to avoid overwriting a new swap folio with
+	 * old compressed data. Only when this is successful can the entry
+	 * be dereferenced.
+	 */
+	tree = swap_zswap_tree(swpentry);
+	if (entry != xa_load(tree, offset)) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (!zswap_decompress(entry, folio)) {
+		ret = -EIO;
+		goto out;
+	}
+
+	xa_erase(tree, offset);
+
+	count_vm_event(ZSWPWB);
+	if (entry->objcg)
+		count_objcg_events(entry->objcg, ZSWPWB, 1);
+
+	zswap_entry_free(entry);
+
+	/* folio is up to date */
+	folio_mark_uptodate(folio);
+
+	/* move it to the tail of the inactive list after end_writeback */
+	folio_set_reclaim(folio);
+
+	/* start writeback */
+	__swap_writepage(folio, NULL);
+
+out:
+	if (ret) {
+		swap_cache_del_folio(folio);
+		folio_unlock(folio);
+	}
+	folio_put(folio);
+	return ret;
+}
+
+/*********************************
+* shrinker functions
+**********************************/
+/*
+ * The dynamic shrinker is modulated by the following factors:
+ *
+ * 1. Each zswap entry has a referenced bit, which the shrinker unsets (giving
+ *    the entry a second chance) before rotating it in the LRU list. If the
+ *    entry is considered again by the shrinker, with its referenced bit unset,
+ *    it is written back. The writeback rate as a result is dynamically
+ *    adjusted by the pool activities - if the pool is dominated by new entries
+ *    (i.e lots of recent zswapouts), these entries will be protected and
+ *    the writeback rate will slow down. On the other hand, if the pool has a
+ *    lot of stagnant entries, these entries will be reclaimed immediately,
+ *    effectively increasing the writeback rate.
+ *
+ * 2. Swapins counter: If we observe swapins, it is a sign that we are
+ *    overshrinking and should slow down. We maintain a swapins counter, which
+ *    is consumed and subtract from the number of eligible objects on the LRU
+ *    in zswap_shrinker_count().
+ *
+ * 3. Compression ratio. The better the workload compresses, the less gains we
+ *    can expect from writeback. We scale down the number of objects available
+ *    for reclaim by this ratio.
+ */
+static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_one *l,
+				       void *arg)
+{
+	struct zswap_entry *entry = container_of(item, struct zswap_entry, lru);
+	bool *encountered_page_in_swapcache = (bool *)arg;
+	swp_entry_t swpentry;
+	enum lru_status ret = LRU_REMOVED_RETRY;
+	int writeback_result;
+
+	/*
+	 * Second chance algorithm: if the entry has its referenced bit set, give it
+	 * a second chance. Only clear the referenced bit and rotate it in the
+	 * zswap's LRU list.
+	 */
+	if (entry->referenced) {
+		entry->referenced = false;
+		return LRU_ROTATE;
+	}
+
+	/*
+	 * As soon as we drop the LRU lock, the entry can be freed by
+	 * a concurrent invalidation. This means the following:
+	 *
+	 * 1. We extract the swp_entry_t to the stack, allowing
+	 *    zswap_writeback_entry() to pin the swap entry and
+	 *    then validate the zswap entry against that swap entry's
+	 *    tree using pointer value comparison. Only when that
+	 *    is successful can the entry be dereferenced.
+	 *
+	 * 2. Usually, objects are taken off the LRU for reclaim. In
+	 *    this case this isn't possible, because if reclaim fails
+	 *    for whatever reason, we have no means of knowing if the
+	 *    entry is alive to put it back on the LRU.
+	 *
+	 *    So rotate it before dropping the lock. If the entry is
+	 *    written back or invalidated, the free path will unlink
+	 *    it. For failures, rotation is the right thing as well.
+	 *
+	 *    Temporary failures, where the same entry should be tried
+	 *    again immediately, almost never happen for this shrinker.
+	 *    We don't do any trylocking; -ENOMEM comes closest,
+	 *    but that's extremely rare and doesn't happen spuriously
+	 *    either. Don't bother distinguishing this case.
+	 */
+	list_move_tail(item, &l->list);
+
+	/*
+	 * Once the lru lock is dropped, the entry might get freed. The
+	 * swpentry is copied to the stack, and entry isn't deref'd again
+	 * until the entry is verified to still be alive in the tree.
+	 */
+	swpentry = entry->swpentry;
+
+	/*
+	 * It's safe to drop the lock here because we return either
+	 * LRU_REMOVED_RETRY, LRU_RETRY or LRU_STOP.
+	 */
+	spin_unlock(&l->lock);
+
+	writeback_result = zswap_writeback_entry(entry, swpentry);
+
+	if (writeback_result) {
+		zswap_reject_reclaim_fail++;
+		ret = LRU_RETRY;
+
+		/*
+		 * Encountering a page already in swap cache is a sign that we are shrinking
+		 * into the warmer region. We should terminate shrinking (if we're in the dynamic
+		 * shrinker context).
+		 */
+		if (writeback_result == -EEXIST && encountered_page_in_swapcache) {
+			ret = LRU_STOP;
+			*encountered_page_in_swapcache = true;
+		}
+	} else {
+		zswap_written_back_pages++;
+	}
+
+	return ret;
+}
+
+static unsigned long zswap_shrinker_scan(struct shrinker *shrinker,
+		struct shrink_control *sc)
+{
+	unsigned long shrink_ret;
+	bool encountered_page_in_swapcache = false;
+
+	if (!zswap_shrinker_enabled ||
+			!mem_cgroup_zswap_writeback_enabled(sc->memcg)) {
+		sc->nr_scanned = 0;
+		return SHRINK_STOP;
+	}
+
+	shrink_ret = list_lru_shrink_walk(&zswap_list_lru, sc, &shrink_memcg_cb,
+		&encountered_page_in_swapcache);
+
+	if (encountered_page_in_swapcache)
+		return SHRINK_STOP;
+
+	return shrink_ret ? shrink_ret : SHRINK_STOP;
+}
+
+static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
+		struct shrink_control *sc)
+{
+	struct mem_cgroup *memcg = sc->memcg;
+	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(sc->nid));
+	atomic_long_t *nr_disk_swapins =
+		&lruvec->zswap_lruvec_state.nr_disk_swapins;
+	unsigned long nr_backing, nr_stored, nr_freeable, nr_disk_swapins_cur,
+		nr_remain;
+
+	if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(memcg))
+		return 0;
+
+	/*
+	 * The shrinker resumes swap writeback, which will enter block
+	 * and may enter fs. XXX: Harmonize with vmscan.c __GFP_FS
+	 * rules (may_enter_fs()), which apply on a per-folio basis.
+	 */
+	if (!gfp_has_io_fs(sc->gfp_mask))
+		return 0;
+
+	/*
+	 * For memcg, use the cgroup-wide ZSWAP stats since we don't
+	 * have them per-node and thus per-lruvec. Careful if memcg is
+	 * runtime-disabled: we can get sc->memcg == NULL, which is ok
+	 * for the lruvec, but not for memcg_page_state().
+	 *
+	 * Without memcg, use the zswap pool-wide metrics.
+	 */
+	if (!mem_cgroup_disabled()) {
+		mem_cgroup_flush_stats(memcg);
+		nr_backing = memcg_page_state(memcg, MEMCG_ZSWAP_B) >> PAGE_SHIFT;
+		nr_stored = memcg_page_state(memcg, MEMCG_ZSWAPPED);
+	} else {
+		nr_backing = zswap_total_pages();
+		nr_stored = atomic_long_read(&zswap_stored_pages);
+	}
+
+	if (!nr_stored)
+		return 0;
+
+	nr_freeable = list_lru_shrink_count(&zswap_list_lru, sc);
+	if (!nr_freeable)
+		return 0;
+
+	/*
+	 * Subtract from the lru size the number of pages that are recently swapped
+	 * in from disk. The idea is that had we protect the zswap's LRU by this
+	 * amount of pages, these disk swapins would not have happened.
+	 */
+	nr_disk_swapins_cur = atomic_long_read(nr_disk_swapins);
+	do {
+		if (nr_freeable >= nr_disk_swapins_cur)
+			nr_remain = 0;
+		else
+			nr_remain = nr_disk_swapins_cur - nr_freeable;
+	} while (!atomic_long_try_cmpxchg(
+		nr_disk_swapins, &nr_disk_swapins_cur, nr_remain));
+
+	nr_freeable -= nr_disk_swapins_cur - nr_remain;
+	if (!nr_freeable)
+		return 0;
+
+	/*
+	 * Scale the number of freeable pages by the memory saving factor.
+	 * This ensures that the better zswap compresses memory, the fewer
+	 * pages we will evict to swap (as it will otherwise incur IO for
+	 * relatively small memory saving).
+	 */
+	return mult_frac(nr_freeable, nr_backing, nr_stored);
+}
+
+static struct shrinker *zswap_alloc_shrinker(void)
+{
+	struct shrinker *shrinker;
+
+	shrinker =
+		shrinker_alloc(SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE, "mm-zswap");
+	if (!shrinker)
+		return NULL;
+
+	shrinker->scan_objects = zswap_shrinker_scan;
+	shrinker->count_objects = zswap_shrinker_count;
+	shrinker->batch = 0;
+	shrinker->seeks = DEFAULT_SEEKS;
+	return shrinker;
+}
+
+static int shrink_memcg(struct mem_cgroup *memcg)
+{
+	int nid, shrunk = 0, scanned = 0;
+
+	if (!mem_cgroup_zswap_writeback_enabled(memcg))
+		return -ENOENT;
+
+	/*
+	 * Skip zombies because their LRUs are reparented and we would be
+	 * reclaiming from the parent instead of the dead memcg.
+	 */
+	if (memcg && !mem_cgroup_online(memcg))
+		return -ENOENT;
+
+	for_each_node_state(nid, N_NORMAL_MEMORY) {
+		unsigned long nr_to_walk = 1;
+
+		shrunk += list_lru_walk_one(&zswap_list_lru, nid, memcg,
+					    &shrink_memcg_cb, NULL, &nr_to_walk);
+		scanned += 1 - nr_to_walk;
+	}
+
+	if (!scanned)
+		return -ENOENT;
+
+	return shrunk ? 0 : -EAGAIN;
+}
+
+static void shrink_worker(struct work_struct *w)
+{
+	struct mem_cgroup *memcg;
+	int ret, failures = 0, attempts = 0;
+	unsigned long thr;
+
+	/* Reclaim down to the accept threshold */
+	thr = zswap_accept_thr_pages();
+
+	/*
+	 * Global reclaim will select cgroup in a round-robin fashion from all
+	 * online memcgs, but memcgs that have no pages in zswap and
+	 * writeback-disabled memcgs (memory.zswap.writeback=0) are not
+	 * candidates for shrinking.
+	 *
+	 * Shrinking will be aborted if we encounter the following
+	 * MAX_RECLAIM_RETRIES times:
+	 * - No writeback-candidate memcgs found in a memcg tree walk.
+	 * - Shrinking a writeback-candidate memcg failed.
+	 *
+	 * We save iteration cursor memcg into zswap_next_shrink,
+	 * which can be modified by the offline memcg cleaner
+	 * zswap_memcg_offline_cleanup().
+	 *
+	 * Since the offline cleaner is called only once, we cannot leave an
+	 * offline memcg reference in zswap_next_shrink.
+	 * We can rely on the cleaner only if we get online memcg under lock.
+	 *
+	 * If we get an offline memcg, we cannot determine if the cleaner has
+	 * already been called or will be called later. We must put back the
+	 * reference before returning from this function. Otherwise, the
+	 * offline memcg left in zswap_next_shrink will hold the reference
+	 * until the next run of shrink_worker().
+	 */
+	do {
+		/*
+		 * Start shrinking from the next memcg after zswap_next_shrink.
+		 * When the offline cleaner has already advanced the cursor,
+		 * advancing the cursor here overlooks one memcg, but this
+		 * should be negligibly rare.
+		 *
+		 * If we get an online memcg, keep the extra reference in case
+		 * the original one obtained by mem_cgroup_iter() is dropped by
+		 * zswap_memcg_offline_cleanup() while we are shrinking the
+		 * memcg.
+		 */
+		spin_lock(&zswap_shrink_lock);
+		do {
+			memcg = mem_cgroup_iter(NULL, zswap_next_shrink, NULL);
+			zswap_next_shrink = memcg;
+		} while (memcg && !mem_cgroup_tryget_online(memcg));
+		spin_unlock(&zswap_shrink_lock);
+
+		if (!memcg) {
+			/*
+			 * Continue shrinking without incrementing failures if
+			 * we found candidate memcgs in the last tree walk.
+			 */
+			if (!attempts && ++failures == MAX_RECLAIM_RETRIES)
+				break;
+
+			attempts = 0;
+			goto resched;
+		}
+
+		ret = shrink_memcg(memcg);
+		/* drop the extra reference */
+		mem_cgroup_put(memcg);
+
+		/*
+		 * There are no writeback-candidate pages in the memcg.
+		 * This is not an issue as long as we can find another memcg
+		 * with pages in zswap. Skip this without incrementing attempts
+		 * and failures.
+		 */
+		if (ret == -ENOENT)
+			continue;
+		++attempts;
+
+		if (ret && ++failures == MAX_RECLAIM_RETRIES)
+			break;
+resched:
+		cond_resched();
+	} while (zswap_total_pages() > thr);
+}
+
+/*********************************
+* main API
+**********************************/
+
+static bool zswap_store_page(struct page *page,
+			     struct obj_cgroup *objcg,
+			     struct zswap_pool *pool)
+{
+	swp_entry_t page_swpentry = page_swap_entry(page);
+	struct zswap_entry *entry, *old;
+
+	/* allocate entry */
+	entry = zswap_entry_cache_alloc(GFP_KERNEL, page_to_nid(page));
+	if (!entry) {
+		zswap_reject_kmemcache_fail++;
+		return false;
+	}
+
+	if (!zswap_compress(page, entry, pool))
+		goto compress_failed;
+
+	old = xa_store(swap_zswap_tree(page_swpentry),
+		       swp_offset(page_swpentry),
+		       entry, GFP_KERNEL);
+	if (xa_is_err(old)) {
+		int err = xa_err(old);
+
+		WARN_ONCE(err != -ENOMEM, "unexpected xarray error: %d\n", err);
+		zswap_reject_alloc_fail++;
+		goto store_failed;
+	}
+
+	/*
+	 * We may have had an existing entry that became stale when
+	 * the folio was redirtied and now the new version is being
+	 * swapped out. Get rid of the old.
+	 */
+	if (old)
+		zswap_entry_free(old);
+
+	/*
+	 * The entry is successfully compressed and stored in the tree, there is
+	 * no further possibility of failure. Grab refs to the pool and objcg,
+	 * charge zswap memory, and increment zswap_stored_pages.
+	 * The opposite actions will be performed by zswap_entry_free()
+	 * when the entry is removed from the tree.
+	 */
+	zswap_pool_get(pool);
+	if (objcg) {
+		obj_cgroup_get(objcg);
+		obj_cgroup_charge_zswap(objcg, entry->length);
+	}
+	atomic_long_inc(&zswap_stored_pages);
+	if (entry->length == PAGE_SIZE)
+		atomic_long_inc(&zswap_stored_incompressible_pages);
+
+	/*
+	 * We finish initializing the entry while it's already in xarray.
+	 * This is safe because:
+	 *
+	 * 1. Concurrent stores and invalidations are excluded by folio lock.
+	 *
+	 * 2. Writeback is excluded by the entry not being on the LRU yet.
+	 *    The publishing order matters to prevent writeback from seeing
+	 *    an incoherent entry.
+	 */
+	entry->pool = pool;
+	entry->swpentry = page_swpentry;
+	entry->objcg = objcg;
+	entry->referenced = true;
+	if (entry->length) {
+		INIT_LIST_HEAD(&entry->lru);
+		zswap_lru_add(&zswap_list_lru, entry);
+	}
+
+	return true;
+
+store_failed:
+	zs_free(pool->zs_pool, entry->handle);
+compress_failed:
+	zswap_entry_cache_free(entry);
+	return false;
+}
+
+bool zswap_store(struct folio *folio)
+{
+	long nr_pages = folio_nr_pages(folio);
+	swp_entry_t swp = folio->swap;
+	struct obj_cgroup *objcg = NULL;
+	struct mem_cgroup *memcg = NULL;
+	struct zswap_pool *pool;
+	bool ret = false;
+	long index;
+
+	VM_WARN_ON_ONCE(!folio_test_locked(folio));
+	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
+
+	if (!zswap_enabled)
+		goto check_old;
+
+	objcg = get_obj_cgroup_from_folio(folio);
+	if (objcg && !obj_cgroup_may_zswap(objcg)) {
+		memcg = get_mem_cgroup_from_objcg(objcg);
+		if (shrink_memcg(memcg)) {
+			mem_cgroup_put(memcg);
+			goto put_objcg;
+		}
+		mem_cgroup_put(memcg);
+	}
+
+	if (zswap_check_limits())
+		goto put_objcg;
+
+	pool = zswap_pool_current_get();
+	if (!pool)
+		goto put_objcg;
+
+	if (objcg) {
+		memcg = get_mem_cgroup_from_objcg(objcg);
+		if (memcg_list_lru_alloc(memcg, &zswap_list_lru, GFP_KERNEL)) {
+			mem_cgroup_put(memcg);
+			goto put_pool;
+		}
+		mem_cgroup_put(memcg);
+	}
+
+	for (index = 0; index < nr_pages; ++index) {
+		struct page *page = folio_page(folio, index);
+
+		if (!zswap_store_page(page, objcg, pool))
+			goto put_pool;
+	}
+
+	if (objcg)
+		count_objcg_events(objcg, ZSWPOUT, nr_pages);
+
+	count_vm_events(ZSWPOUT, nr_pages);
+
+	ret = true;
+
+put_pool:
+	zswap_pool_put(pool);
+put_objcg:
+	obj_cgroup_put(objcg);
+	if (!ret && zswap_pool_reached_full)
+		queue_work(shrink_wq, &zswap_shrink_work);
+check_old:
+	/*
+	 * If the zswap store fails or zswap is disabled, we must invalidate
+	 * the possibly stale entries which were previously stored at the
+	 * offsets corresponding to each page of the folio. Otherwise,
+	 * writeback could overwrite the new data in the swapfile.
+	 */
+	if (!ret) {
+		unsigned type = swp_type(swp);
+		pgoff_t offset = swp_offset(swp);
+		struct zswap_entry *entry;
+		struct xarray *tree;
+
+		for (index = 0; index < nr_pages; ++index) {
+			tree = swap_zswap_tree(swp_entry(type, offset + index));
+			entry = xa_erase(tree, offset + index);
+			if (entry)
+				zswap_entry_free(entry);
+		}
+	}
+
+	return ret;
+}
+
+/**
+ * zswap_load() - load a folio from zswap
+ * @folio: folio to load
+ *
+ * Return: 0 on success, with the folio unlocked and marked up-to-date, or one
+ * of the following error codes:
+ *
+ *  -EIO: if the swapped out content was in zswap, but could not be loaded
+ *  into the page due to a decompression failure. The folio is unlocked, but
+ *  NOT marked up-to-date, so that an IO error is emitted (e.g. do_swap_page()
+ *  will SIGBUS).
+ *
+ *  -EINVAL: if the swapped out content was in zswap, but the page belongs
+ *  to a large folio, which is not supported by zswap. The folio is unlocked,
+ *  but NOT marked up-to-date, so that an IO error is emitted (e.g.
+ *  do_swap_page() will SIGBUS).
+ *
+ *  -ENOENT: if the swapped out content was not in zswap. The folio remains
+ *  locked on return.
+ */
+int zswap_load(struct folio *folio)
+{
+	swp_entry_t swp = folio->swap;
+	pgoff_t offset = swp_offset(swp);
+	struct xarray *tree = swap_zswap_tree(swp);
+	struct zswap_entry *entry;
+
+	VM_WARN_ON_ONCE(!folio_test_locked(folio));
+	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
+
+	if (zswap_never_enabled())
+		return -ENOENT;
+
+	/*
+	 * Large folios should not be swapped in while zswap is being used, as
+	 * they are not properly handled. Zswap does not properly load large
+	 * folios, and a large folio may only be partially in zswap.
+	 */
+	if (WARN_ON_ONCE(folio_test_large(folio))) {
+		folio_unlock(folio);
+		return -EINVAL;
+	}
+
+	entry = xa_load(tree, offset);
+	if (!entry)
+		return -ENOENT;
+
+	if (!zswap_decompress(entry, folio)) {
+		folio_unlock(folio);
+		return -EIO;
+	}
+
+	folio_mark_uptodate(folio);
+
+	count_vm_event(ZSWPIN);
+	if (entry->objcg)
+		count_objcg_events(entry->objcg, ZSWPIN, 1);
+
+	/*
+	 * We are reading into the swapcache, invalidate zswap entry.
+	 * The swapcache is the authoritative owner of the page and
+	 * its mappings, and the pressure that results from having two
+	 * in-memory copies outweighs any benefits of caching the
+	 * compression work.
+	 */
+	folio_mark_dirty(folio);
+	xa_erase(tree, offset);
+	zswap_entry_free(entry);
+
+	folio_unlock(folio);
+	return 0;
+}
+
+void zswap_invalidate(swp_entry_t swp)
+{
+	pgoff_t offset = swp_offset(swp);
+	struct xarray *tree = swap_zswap_tree(swp);
+	struct zswap_entry *entry;
+
+	if (xa_empty(tree))
+		return;
+
+	entry = xa_erase(tree, offset);
+	if (entry)
+		zswap_entry_free(entry);
+}
+
+int zswap_swapon(int type, unsigned long nr_pages)
+{
+	struct xarray *trees, *tree;
+	unsigned int nr, i;
+
+	nr = DIV_ROUND_UP(nr_pages, ZSWAP_ADDRESS_SPACE_PAGES);
+	trees = kvzalloc_objs(*tree, nr);
+	if (!trees) {
+		pr_err("alloc failed, zswap disabled for swap type %d\n", type);
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < nr; i++)
+		xa_init(trees + i);
+
+	nr_zswap_trees[type] = nr;
+	zswap_trees[type] = trees;
+	return 0;
+}
+
+void zswap_swapoff(int type)
+{
+	struct xarray *trees = zswap_trees[type];
+	unsigned int i;
+
+	if (!trees)
+		return;
+
+	/* try_to_unuse() invalidated all the entries already */
+	for (i = 0; i < nr_zswap_trees[type]; i++)
+		WARN_ON_ONCE(!xa_empty(trees + i));
+
+	kvfree(trees);
+	nr_zswap_trees[type] = 0;
+	zswap_trees[type] = NULL;
+}
+
+/*********************************
+* debugfs functions
+**********************************/
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+
+static struct dentry *zswap_debugfs_root;
+
+static int debugfs_get_total_size(void *data, u64 *val)
+{
+	*val = zswap_total_pages() * PAGE_SIZE;
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(total_size_fops, debugfs_get_total_size, NULL, "%llu\n");
+
+static int debugfs_get_stored_pages(void *data, u64 *val)
+{
+	*val = atomic_long_read(&zswap_stored_pages);
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(stored_pages_fops, debugfs_get_stored_pages, NULL, "%llu\n");
+
+static int debugfs_get_stored_incompressible_pages(void *data, u64 *val)
+{
+	*val = atomic_long_read(&zswap_stored_incompressible_pages);
+	return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(stored_incompressible_pages_fops,
+		debugfs_get_stored_incompressible_pages, NULL, "%llu\n");
+
+static int zswap_debugfs_init(void)
+{
+	if (!debugfs_initialized())
+		return -ENODEV;
+
+	zswap_debugfs_root = debugfs_create_dir("zswap", NULL);
+
+	debugfs_create_u64("pool_limit_hit", 0444,
+			   zswap_debugfs_root, &zswap_pool_limit_hit);
+	debugfs_create_u64("reject_reclaim_fail", 0444,
+			   zswap_debugfs_root, &zswap_reject_reclaim_fail);
+	debugfs_create_u64("reject_alloc_fail", 0444,
+			   zswap_debugfs_root, &zswap_reject_alloc_fail);
+	debugfs_create_u64("reject_kmemcache_fail", 0444,
+			   zswap_debugfs_root, &zswap_reject_kmemcache_fail);
+	debugfs_create_u64("reject_compress_fail", 0444,
+			   zswap_debugfs_root, &zswap_reject_compress_fail);
+	debugfs_create_u64("reject_compress_poor", 0444,
+			   zswap_debugfs_root, &zswap_reject_compress_poor);
+	debugfs_create_u64("decompress_fail", 0444,
+			   zswap_debugfs_root, &zswap_decompress_fail);
+	debugfs_create_u64("written_back_pages", 0444,
+			   zswap_debugfs_root, &zswap_written_back_pages);
+	debugfs_create_file("pool_total_size", 0444,
+			    zswap_debugfs_root, NULL, &total_size_fops);
+	debugfs_create_file("stored_pages", 0444,
+			    zswap_debugfs_root, NULL, &stored_pages_fops);
+	debugfs_create_file("stored_incompressible_pages", 0444,
+			    zswap_debugfs_root, NULL,
+			    &stored_incompressible_pages_fops);
+
+	return 0;
+}
+#else
+static int zswap_debugfs_init(void)
+{
+	return 0;
+}
+#endif
+
+/*********************************
+* module init and exit
+**********************************/
+static int zswap_setup(void)
+{
+	struct zswap_pool *pool;
+	int ret;
+
+	zswap_entry_cache = KMEM_CACHE(zswap_entry, 0);
+	if (!zswap_entry_cache) {
+		pr_err("entry cache creation failed\n");
+		goto cache_fail;
+	}
+
+	ret = cpuhp_setup_state_multi(CPUHP_MM_ZSWP_POOL_PREPARE,
+				      "mm/zswap_pool:prepare",
+				      zswap_cpu_comp_prepare,
+				      NULL);
+	if (ret)
+		goto hp_fail;
+
+	shrink_wq = alloc_workqueue("zswap-shrink",
+			WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
+	if (!shrink_wq)
+		goto shrink_wq_fail;
+
+	zswap_shrinker = zswap_alloc_shrinker();
+	if (!zswap_shrinker)
+		goto shrinker_fail;
+	if (list_lru_init_memcg(&zswap_list_lru, zswap_shrinker))
+		goto lru_fail;
+	shrinker_register(zswap_shrinker);
+
+	INIT_WORK(&zswap_shrink_work, shrink_worker);
+
+	pool = __zswap_pool_create_fallback();
+	if (pool) {
+		pr_info("loaded using pool %s\n", pool->tfm_name);
+		list_add(&pool->list, &zswap_pools);
+		zswap_has_pool = true;
+		static_branch_enable(&zswap_ever_enabled);
+	} else {
+		pr_err("pool creation failed\n");
+		zswap_enabled = false;
+	}
+
+	if (zswap_debugfs_init())
+		pr_warn("debugfs initialization failed\n");
+	zswap_init_state = ZSWAP_INIT_SUCCEED;
+	return 0;
+
+lru_fail:
+	shrinker_free(zswap_shrinker);
+shrinker_fail:
+	destroy_workqueue(shrink_wq);
+shrink_wq_fail:
+	cpuhp_remove_multi_state(CPUHP_MM_ZSWP_POOL_PREPARE);
+hp_fail:
+	kmem_cache_destroy(zswap_entry_cache);
+cache_fail:
+	/* if built-in, we aren't unloaded on failure; don't allow use */
+	zswap_init_state = ZSWAP_INIT_FAILED;
+	zswap_enabled = false;
+	return -ENOMEM;
+}
+
+static int __init zswap_init(void)
+{
+	if (!zswap_enabled)
+		return 0;
+	return zswap_setup();
+}
+/* must be late so crypto has time to come up */
+late_initcall(zswap_init);
+
+MODULE_AUTHOR("Seth Jennings <sjennings@variantweb.net>");
+MODULE_DESCRIPTION("Compressed cache for swap pages");