sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

1 files changed, 702 insertions, 0 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
new file mode 100644
index 000000000..88962571c
--- /dev/null
+++ b/mm/page_io.c
@@ -0,0 +1,702 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/mm/page_io.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *
+ *  Swap reorganised 29.12.95, 
+ *  Asynchronous swapping added 30.12.95. Stephen Tweedie
+ *  Removed race in async swapping. 14.4.1996. Bruno Haible
+ *  Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
+ *  Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
+ */
+
+#include <linux/mm.h>
+#include <linux/kernel_stat.h>
+#include <linux/gfp.h>
+#include <linux/pagemap.h>
+#include <linux/swap.h>
+#include <linux/bio.h>
+#include <linux/swapops.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
+#include <linux/psi.h>
+#include <linux/uio.h>
+#include <linux/sched/task.h>
+#include <linux/delayacct.h>
+#include <linux/zswap.h>
+#include <linux/swap_ops.h>
+#include "swap.h"
+#include "swap_table.h"
+
+int generic_swapfile_activate(struct swap_info_struct *sis,
+				struct file *swap_file,
+				sector_t *span)
+{
+	struct address_space *mapping = swap_file->f_mapping;
+	struct inode *inode = mapping->host;
+	unsigned blocks_per_page;
+	unsigned long page_no;
+	unsigned blkbits;
+	sector_t probe_block;
+	sector_t last_block;
+	sector_t lowest_block = -1;
+	sector_t highest_block = 0;
+	int nr_extents = 0;
+	int ret;
+
+	blkbits = inode->i_blkbits;
+	blocks_per_page = PAGE_SIZE >> blkbits;
+
+	/*
+	 * Map all the blocks into the extent tree.  This code doesn't try
+	 * to be very smart.
+	 */
+	probe_block = 0;
+	page_no = 0;
+	last_block = i_size_read(inode) >> blkbits;
+	while ((probe_block + blocks_per_page) <= last_block &&
+			page_no < sis->max) {
+		unsigned block_in_page;
+		sector_t first_block;
+
+		cond_resched();
+
+		first_block = probe_block;
+		ret = bmap(inode, &first_block);
+		if (ret || !first_block)
+			goto bad_bmap;
+
+		/*
+		 * It must be PAGE_SIZE aligned on-disk
+		 */
+		if (first_block & (blocks_per_page - 1)) {
+			probe_block++;
+			goto reprobe;
+		}
+
+		for (block_in_page = 1; block_in_page < blocks_per_page;
+					block_in_page++) {
+			sector_t block;
+
+			block = probe_block + block_in_page;
+			ret = bmap(inode, &block);
+			if (ret || !block)
+				goto bad_bmap;
+
+			if (block != first_block + block_in_page) {
+				/* Discontiguity */
+				probe_block++;
+				goto reprobe;
+			}
+		}
+
+		first_block >>= (PAGE_SHIFT - blkbits);
+		if (page_no) {	/* exclude the header page */
+			if (first_block < lowest_block)
+				lowest_block = first_block;
+			if (first_block > highest_block)
+				highest_block = first_block;
+		}
+
+		/*
+		 * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
+		 */
+		ret = add_swap_extent(sis, page_no, 1, first_block);
+		if (ret < 0)
+			goto out;
+		nr_extents += ret;
+		page_no++;
+		probe_block += blocks_per_page;
+reprobe:
+		continue;
+	}
+	ret = nr_extents;
+	*span = 1 + highest_block - lowest_block;
+	if (page_no == 0)
+		page_no = 1;	/* force Empty message */
+	sis->max = page_no;
+	sis->pages = page_no - 1;
+out:
+	return ret;
+bad_bmap:
+	pr_err("swapon: swapfile has holes\n");
+	ret = -EINVAL;
+	goto out;
+}
+
+static bool is_folio_zero_filled(struct folio *folio)
+{
+	unsigned int pos, last_pos;
+	unsigned long *data;
+	unsigned int i;
+
+	last_pos = PAGE_SIZE / sizeof(*data) - 1;
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		data = kmap_local_folio(folio, i * PAGE_SIZE);
+		/*
+		 * Check last word first, incase the page is zero-filled at
+		 * the start and has non-zero data at the end, which is common
+		 * in real-world workloads.
+		 */
+		if (data[last_pos]) {
+			kunmap_local(data);
+			return false;
+		}
+		for (pos = 0; pos < last_pos; pos++) {
+			if (data[pos]) {
+				kunmap_local(data);
+				return false;
+			}
+		}
+		kunmap_local(data);
+	}
+
+	return true;
+}
+
+static void swap_zeromap_folio_set(struct folio *folio)
+{
+	struct obj_cgroup *objcg = get_obj_cgroup_from_folio(folio);
+	int nr_pages = folio_nr_pages(folio);
+	struct swap_cluster_info *ci;
+	swp_entry_t entry;
+	unsigned int i;
+
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio);
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+
+	ci = swap_cluster_get_and_lock(folio);
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		entry = page_swap_entry(folio_page(folio, i));
+		__swap_table_set_zero(ci, swp_cluster_offset(entry));
+	}
+	swap_cluster_unlock(ci);
+
+	count_vm_events(SWPOUT_ZERO, nr_pages);
+	if (objcg) {
+		count_objcg_events(objcg, SWPOUT_ZERO, nr_pages);
+		obj_cgroup_put(objcg);
+	}
+}
+
+static void swap_zeromap_folio_clear(struct folio *folio)
+{
+	struct swap_cluster_info *ci;
+	swp_entry_t entry;
+	unsigned int i;
+
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio);
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+
+	ci = swap_cluster_get_and_lock(folio);
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		entry = page_swap_entry(folio_page(folio, i));
+		__swap_table_clear_zero(ci, swp_cluster_offset(entry));
+	}
+	swap_cluster_unlock(ci);
+}
+
+/*
+ * We may have stale swap cache pages in memory: notice
+ * them here and get rid of the unnecessary final write.
+ */
+int swap_writeout(struct swap_io_ctx *ctx, struct folio *folio)
+{
+	int ret = 0;
+
+	if (folio_free_swap(folio))
+		goto out_unlock;
+
+	/*
+	 * Arch code may have to preserve more data than just the page
+	 * contents, e.g. memory tags.
+	 */
+	ret = arch_prepare_to_swap(folio);
+	if (ret) {
+		folio_mark_dirty(folio);
+		goto out_unlock;
+	}
+
+	/*
+	 * Use the swap table zero mark to avoid doing IO for zero-filled
+	 * pages. The zero mark is protected by the cluster lock, which is
+	 * acquired internally by swap_zeromap_folio_set/clear.
+	 */
+	if (is_folio_zero_filled(folio)) {
+		swap_zeromap_folio_set(folio);
+		goto out_unlock;
+	}
+
+	/*
+	 * Clear bits this folio occupies in the zeromap to prevent zero data
+	 * being read in from any previous zero writes that occupied the same
+	 * swap entries.
+	 */
+	swap_zeromap_folio_clear(folio);
+
+	if (zswap_store(folio)) {
+		count_mthp_stat(folio_order(folio), MTHP_STAT_ZSWPOUT);
+		goto out_unlock;
+	}
+
+	rcu_read_lock();
+	if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
+		rcu_read_unlock();
+		folio_mark_dirty(folio);
+		return AOP_WRITEPAGE_ACTIVATE;
+	}
+	rcu_read_unlock();
+
+	__swap_writepage(ctx, folio);
+	return 0;
+out_unlock:
+	folio_unlock(folio);
+	return ret;
+}
+
+#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
+static struct cgroup_subsys_state *folio_memcg_blkg_css(struct folio *folio)
+{
+	return cgroup_e_css(folio_memcg(folio)->css.cgroup, &io_cgrp_subsys);
+}
+
+static bool folio_blkg_can_merge(struct folio *folio, struct folio *prev_folio)
+{
+	bool can_merge = true;
+
+	if (folio_memcg_charged(folio) != folio_memcg_charged(prev_folio))
+		return false;
+	if (folio_memcg_charged(folio)) {
+		rcu_read_lock();
+		if (folio_memcg_blkg_css(folio) !=
+		    folio_memcg_blkg_css(prev_folio))
+			can_merge = false;
+		rcu_read_unlock();
+	}
+	return can_merge;
+}
+
+static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
+{
+	struct cgroup_subsys_state *css;
+
+	if (!folio_memcg_charged(folio))
+		return;
+	rcu_read_lock();
+	css = folio_memcg_blkg_css(folio);
+	if (css && !css_tryget(css))
+		css = NULL;
+	rcu_read_unlock();
+
+	bio_associate_blkg_from_css(bio, css);
+	if (css)
+		css_put(css);
+}
+#else
+static bool folio_blkg_can_merge(struct folio *folio, struct folio *prev_folio)
+{
+	return true;
+}
+#define bio_associate_blkg_from_page(bio, folio)		do { } while (0)
+#endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
+
+static mempool_t *sio_pool;
+
+int sio_pool_init(void)
+{
+	if (!sio_pool) {
+		mempool_t *pool = mempool_create_kmalloc_pool(
+			SWAP_CLUSTER_MAX, sizeof(struct swap_iocb));
+		if (cmpxchg(&sio_pool, NULL, pool))
+			mempool_destroy(pool);
+	}
+	if (!sio_pool)
+		return -ENOMEM;
+	return 0;
+}
+
+static bool swap_can_merge(struct swap_io_ctx *ctx, struct folio *folio,
+		int rw)
+{
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
+	struct bio_vec *last_bv = &ctx->sio->bvecs[ctx->sio->nr_bvecs - 1];
+	struct folio *prev_folio = bvec_folio(last_bv);
+	size_t prev_folio_size = folio_size(prev_folio);
+
+	if (ctx->sis != sis)
+		return false;
+	return sis->ops->can_merge(folio, prev_folio, prev_folio_size, rw);
+}
+
+static void swap_add_folio(struct swap_io_ctx *ctx, struct folio *folio, int rw)
+{
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
+	struct swap_iocb *sio = ctx->sio;
+
+	if (sio && !swap_can_merge(ctx, folio, rw)) {
+		if (rw == WRITE)
+			swap_write_submit(ctx);
+		else
+			swap_read_submit(ctx);
+		sio = ctx->sio;
+	}
+
+	if (!sio) {
+		ctx->sis = sis;
+		ctx->sio = sio = mempool_alloc(sio_pool, GFP_NOIO);
+		sio->nr_bvecs = 0;
+		sio->len = 0;
+	}
+	bvec_set_folio(&sio->bvecs[sio->nr_bvecs], folio, folio_size(folio), 0);
+	sio->len += folio_size(folio);
+
+	/*
+	 * Write out the iocb if we filled it, or if the device is synchronous.
+	 *
+	 * The latter is to work around expectations in the classic LRU code
+	 * which make synchronous clearing of the folio writeback flag in the
+	 * reclaim path beneficial.
+	 */
+	if (++sio->nr_bvecs == ARRAY_SIZE(sio->bvecs) ||
+	    (rw == WRITE && (sis->flags & SWP_SYNCHRONOUS_IO))) {
+		if (rw == WRITE)
+			swap_write_submit(ctx);
+		else
+			swap_read_submit(ctx);
+	}
+}
+
+void __swap_writepage(struct swap_io_ctx *ctx, struct folio *folio)
+{
+	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	if (unlikely(folio_test_pmd_mappable(folio))) {
+		count_memcg_folio_events(folio, THP_SWPOUT, 1);
+		count_vm_event(THP_SWPOUT);
+	}
+#endif
+	count_mthp_stat(folio_order(folio), MTHP_STAT_SWPOUT);
+	count_memcg_folio_events(folio, PSWPOUT, folio_nr_pages(folio));
+	count_vm_events(PSWPOUT, folio_nr_pages(folio));
+
+	folio_start_writeback(folio);
+	folio_unlock(folio);
+	swap_add_folio(ctx, folio, WRITE);
+}
+
+/*
+ * Return the count of contiguous swap entries that share the same
+ * zeromap status as the starting entry. If is_zerop is not NULL,
+ * it will return the zeromap status of the starting entry.
+ *
+ * Context: Caller must ensure the cluster containing the entries
+ * that will be checked won't be freed.
+ */
+static int swap_zeromap_batch(swp_entry_t entry, int max_nr,
+			      bool *is_zerop)
+{
+	int i;
+	bool is_zero;
+	unsigned int ci_start = swp_cluster_offset(entry);
+	struct swap_cluster_info *ci = __swap_entry_to_cluster(entry);
+
+	VM_WARN_ON_ONCE(ci_start + max_nr > SWAPFILE_CLUSTER);
+
+	rcu_read_lock();
+	is_zero = __swap_table_test_zero(ci, ci_start);
+	for (i = 1; i < max_nr; i++)
+		if (is_zero != __swap_table_test_zero(ci, ci_start + i))
+			break;
+	rcu_read_unlock();
+	if (is_zerop)
+		*is_zerop = is_zero;
+
+	return i;
+}
+
+static bool swap_read_folio_zeromap(struct folio *folio)
+{
+	int nr_pages = folio_nr_pages(folio);
+	struct obj_cgroup *objcg;
+	bool is_zeromap;
+
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+
+	/*
+	 * Swapping in a large folio that is partially in the zeromap is not
+	 * currently handled. Return true without marking the folio uptodate so
+	 * that an IO error is emitted (e.g. do_swap_page() will sigbus).
+	 * Folio lock stabilizes the cluster and map, so the check is safe.
+	 */
+	if (WARN_ON_ONCE(swap_zeromap_batch(folio->swap, nr_pages,
+			 &is_zeromap) != nr_pages))
+		return true;
+
+	if (!is_zeromap)
+		return false;
+
+	objcg = get_obj_cgroup_from_folio(folio);
+	count_vm_events(SWPIN_ZERO, nr_pages);
+	if (objcg) {
+		count_objcg_events(objcg, SWPIN_ZERO, nr_pages);
+		obj_cgroup_put(objcg);
+	}
+
+	folio_zero_range(folio, 0, folio_size(folio));
+	folio_mark_uptodate(folio);
+	return true;
+}
+
+void swap_read_folio(struct swap_io_ctx *ctx, struct folio *folio)
+{
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
+	bool synchronous = sis->flags & SWP_SYNCHRONOUS_IO;
+	bool workingset = folio_test_workingset(folio);
+	unsigned long pflags;
+	bool in_thrashing;
+
+	VM_BUG_ON_FOLIO(!folio_test_swapcache(folio) && !synchronous, folio);
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio);
+
+	/*
+	 * Count submission time as memory stall and delay. When the device
+	 * is congested, or the submitting cgroup IO-throttled, submission
+	 * can be a significant part of overall IO time.
+	 */
+	if (workingset) {
+		delayacct_thrashing_start(&in_thrashing);
+		psi_memstall_enter(&pflags);
+	}
+	delayacct_swapin_start();
+
+	if (swap_read_folio_zeromap(folio)) {
+		folio_unlock(folio);
+		goto finish;
+	}
+
+	if (zswap_load(folio) != -ENOENT)
+		goto finish;
+
+	/* We have to read from slower devices. Increase zswap protection. */
+	zswap_folio_swapin(folio);
+	swap_add_folio(ctx, folio, READ);
+
+finish:
+	if (workingset) {
+		delayacct_thrashing_end(&in_thrashing);
+		psi_memstall_leave(&pflags);
+	}
+	delayacct_swapin_end();
+}
+
+static void swap_write_end(struct swap_iocb *sio, bool failed)
+{
+	int p;
+
+	for (p = 0; p < sio->nr_bvecs; p++) {
+		struct page *page = sio->bvecs[p].bv_page;
+
+		if (failed) {
+			set_page_dirty(page);
+			ClearPageReclaim(page);
+		}
+		end_page_writeback(page);
+	}
+	mempool_free(sio, sio_pool);
+}
+
+static void swap_fs_write_complete(struct kiocb *iocb, long ret)
+{
+	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
+	bool failed = ret != sio->len;
+
+	if (failed) {
+		struct page *page = sio->bvecs[0].bv_page;
+
+		/*
+		 * In the case of swap-over-nfs, this can be a temporary failure
+		 * if the system has limited memory for allocating transmit
+		 * buffers.  Mark the page dirty and avoid
+		 * folio_rotate_reclaimable but rate-limit the messages.
+		 */
+		pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
+				   ret, swap_dev_pos(page_swap_entry(page)));
+	}
+
+	swap_write_end(sio, failed);
+}
+
+static void end_swap_bio_write(struct bio *bio)
+{
+	struct swap_iocb *sio = container_of(bio, struct swap_iocb, bio);
+	bool failed = !!bio->bi_status;
+
+	if (failed)
+		pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
+				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
+				     (unsigned long long)bio->bi_iter.bi_sector);
+	bio_uninit(bio);
+	swap_write_end(sio, failed);
+}
+
+static void swap_read_end(struct swap_iocb *sio, bool failed)
+{
+	int p;
+
+	for (p = 0; p < sio->nr_bvecs; p++) {
+		struct folio *folio = bvec_folio(&sio->bvecs[p]);
+
+		if (!failed) {
+			count_mthp_stat(folio_order(folio), MTHP_STAT_SWPIN);
+			count_memcg_folio_events(folio, PSWPIN,
+					folio_nr_pages(folio));
+			folio_mark_uptodate(folio);
+		}
+		folio_unlock(folio);
+	}
+
+	if (!failed)
+		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
+
+	mempool_free(sio, sio_pool);
+}
+
+static void swap_fs_read_complete(struct kiocb *iocb, long ret)
+{
+	struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
+	bool failed = ret != sio->len;
+
+	if (failed)
+		pr_alert_ratelimited("Read-error on swap-device\n");
+	swap_read_end(sio, failed);
+}
+
+static void swap_bio_read_end_io(struct bio *bio)
+{
+	struct swap_iocb *sio = container_of(bio, struct swap_iocb, bio);
+	bool failed = !!bio->bi_status;
+
+	if (failed)
+		pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
+				     MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
+				     (unsigned long long)bio->bi_iter.bi_sector);
+	bio_uninit(bio);
+	swap_read_end(sio, failed);
+}
+
+static void swap_bdev_submit_write(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct bio *bio = &sio->bio;
+
+	bio_init(bio, ctx->sis->bdev, sio->bvecs, ARRAY_SIZE(sio->bvecs),
+			REQ_OP_WRITE | REQ_SWAP);
+	bio->bi_iter.bi_size = sio->len;
+	bio->bi_iter.bi_sector = swap_folio_sector(bio_first_folio_all(bio));
+	bio_associate_blkg_from_page(bio, bio_first_folio_all(bio));
+
+	if (ctx->sis->flags & SWP_SYNCHRONOUS_IO) {
+		submit_bio_wait(bio);
+		end_swap_bio_write(bio);
+	} else {
+		bio->bi_end_io = end_swap_bio_write;
+		submit_bio(bio);
+	}
+}
+
+static void swap_bdev_submit_read(struct swap_io_ctx *ctx)
+{
+	struct swap_iocb *sio = ctx->sio;
+	struct bio *bio = &sio->bio;
+
+	bio_init(bio, ctx->sis->bdev, sio->bvecs, ARRAY_SIZE(sio->bvecs),
+			REQ_OP_READ);
+	bio->bi_iter.bi_size = sio->len;
+	bio->bi_iter.bi_sector = swap_folio_sector(bio_first_folio_all(bio));
+
+	if (ctx->sis->flags & SWP_SYNCHRONOUS_IO) {
+		/*
+		 * Keep this task valid during swap readpage because the oom
+		 * killer may attempt to access it in the page fault retry
+		 * time check.
+		 */
+		get_task_struct(current);
+		submit_bio_wait(bio);
+		swap_bio_read_end_io(bio);
+		put_task_struct(current);
+	} else {
+		bio->bi_end_io = swap_bio_read_end_io;
+		submit_bio(bio);
+	}
+}
+
+static bool swap_bdev_can_merge(struct folio *folio, struct folio *prev_folio,
+		size_t prev_folio_size, int rw)
+{
+	if (swap_folio_sector(folio) !=
+	    swap_folio_sector(prev_folio) + (prev_folio_size >> SECTOR_SHIFT))
+		return false;
+	if (rw == WRITE && !folio_blkg_can_merge(folio, prev_folio))
+		return false;
+	return true;
+}
+
+const struct swap_ops swap_bdev_ops = {
+	.submit_write		= swap_bdev_submit_write,
+	.submit_read		= swap_bdev_submit_read,
+	.can_merge		= swap_bdev_can_merge,
+};
+
+void swap_fs_prepare_rw(struct swap_io_ctx *ctx, int rw, struct iov_iter *iter)
+{
+	struct swap_iocb *sio = ctx->sio;
+
+	init_sync_kiocb(&sio->iocb, ctx->sis->swap_file);
+	sio->iocb.ki_pos = swap_dev_pos(bvec_folio(&sio->bvecs[0])->swap);
+	if (rw == WRITE)
+		sio->iocb.ki_complete = swap_fs_write_complete;
+	else
+		sio->iocb.ki_complete = swap_fs_read_complete;
+
+	iov_iter_bvec(iter, rw == WRITE ? ITER_SOURCE : ITER_DEST,
+			sio->bvecs, sio->nr_bvecs, sio->len);
+}
+EXPORT_SYMBOL_GPL(swap_fs_prepare_rw);
+
+bool swap_fs_can_merge(struct folio *folio, struct folio *prev_folio,
+		size_t prev_folio_size, int rw)
+{
+	return swap_dev_pos(folio->swap) ==
+		swap_dev_pos(prev_folio->swap) + prev_folio_size;
+}
+EXPORT_SYMBOL_GPL(swap_fs_can_merge);
+
+int swap_fs_activate(struct swap_info_struct *sis, const struct swap_ops *ops)
+{
+	sis->ops = ops;
+	return add_swap_extent(sis, 0, sis->max, 0);
+}
+EXPORT_SYMBOL_GPL(swap_fs_activate);
+
+void swap_write_submit(struct swap_io_ctx *ctx)
+{
+	if (!ctx->sio)
+		return;
+	count_vm_events(NRSWPOUT, 1);
+	ctx->sis->ops->submit_write(ctx);
+	ctx->sio = NULL;
+	ctx->sis = NULL;
+}
+
+void swap_read_submit(struct swap_io_ctx *ctx)
+{
+	if (!ctx->sio)
+		return;
+	count_vm_events(NRSWPIN, 1);
+	ctx->sis->ops->submit_read(ctx);
+	ctx->sio = NULL;
+	ctx->sis = NULL;
+}