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, 3958 insertions, 0 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
new file mode 100644
index 000000000..601979b97
--- /dev/null
+++ b/mm/swapfile.c
@@ -0,0 +1,3958 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/mm/swapfile.c
+ *
+ *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
+ *  Swap reorganised 29.12.95, Stephen Tweedie
+ */
+
+#include <linux/blkdev.h>
+#include <linux/mm.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
+#include <linux/hugetlb.h>
+#include <linux/mman.h>
+#include <linux/slab.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/vmalloc.h>
+#include <linux/pagemap.h>
+#include <linux/namei.h>
+#include <linux/shmem_fs.h>
+#include <linux/blk-cgroup.h>
+#include <linux/random.h>
+#include <linux/writeback.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/init.h>
+#include <linux/ksm.h>
+#include <linux/rmap.h>
+#include <linux/security.h>
+#include <linux/backing-dev.h>
+#include <linux/mutex.h>
+#include <linux/capability.h>
+#include <linux/syscalls.h>
+#include <linux/memcontrol.h>
+#include <linux/poll.h>
+#include <linux/oom.h>
+#include <linux/swapfile.h>
+#include <linux/export.h>
+#include <linux/sort.h>
+#include <linux/completion.h>
+#include <linux/suspend.h>
+#include <linux/zswap.h>
+#include <linux/plist.h>
+
+#include <asm/tlbflush.h>
+#include <linux/leafops.h>
+#include "swap_table.h"
+#include "internal.h"
+#include "swap.h"
+
+static void swap_range_alloc(struct swap_info_struct *si,
+			     unsigned int nr_entries);
+static bool folio_swapcache_freeable(struct folio *folio);
+static void move_cluster(struct swap_info_struct *si,
+			 struct swap_cluster_info *ci, struct list_head *list,
+			 enum swap_cluster_flags new_flags);
+
+/*
+ * Protects the swap_info array, and the SWP_USED flag. swap_info contains
+ * lazily allocated & freed swap device info struts, and SWP_USED indicates
+ * which device is used, ~SWP_USED devices and can be reused.
+ *
+ * Also protects swap_active_head total_swap_pages, and the SWP_WRITEOK flag.
+ */
+static DEFINE_SPINLOCK(swap_lock);
+static unsigned int nr_swapfiles;
+atomic_long_t nr_swap_pages;
+/*
+ * Some modules use swappable objects and may try to swap them out under
+ * memory pressure (via the shrinker). Before doing so, they may wish to
+ * check to see if any swap space is available.
+ */
+EXPORT_SYMBOL_GPL(nr_swap_pages);
+/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
+long total_swap_pages;
+#define DEF_SWAP_PRIO  -1
+unsigned long swapfile_maximum_size;
+#ifdef CONFIG_MIGRATION
+bool swap_migration_ad_supported;
+#endif	/* CONFIG_MIGRATION */
+
+static const char Bad_file[] = "Bad swap file entry ";
+static const char Bad_offset[] = "Bad swap offset entry ";
+
+/*
+ * all active swap_info_structs
+ * protected with swap_lock, and ordered by priority.
+ */
+static PLIST_HEAD(swap_active_head);
+
+/*
+ * all available (active, not full) swap_info_structs
+ * protected with swap_avail_lock, ordered by priority.
+ * This is used by folio_alloc_swap() instead of swap_active_head
+ * because swap_active_head includes all swap_info_structs,
+ * but folio_alloc_swap() doesn't need to look at full ones.
+ * This uses its own lock instead of swap_lock because when a
+ * swap_info_struct changes between not-full/full, it needs to
+ * add/remove itself to/from this list, but the swap_info_struct->lock
+ * is held and the locking order requires swap_lock to be taken
+ * before any swap_info_struct->lock.
+ */
+static PLIST_HEAD(swap_avail_head);
+static DEFINE_SPINLOCK(swap_avail_lock);
+
+struct swap_info_struct *swap_info[MAX_SWAPFILES];
+
+static struct kmem_cache *swap_table_cachep;
+
+/* Protects si->swap_file for /proc/swaps usage */
+static DEFINE_MUTEX(swapon_mutex);
+
+static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
+/* Activity counter to indicate that a swapon or swapoff has occurred */
+static atomic_t proc_poll_event = ATOMIC_INIT(0);
+
+atomic_t nr_rotate_swap = ATOMIC_INIT(0);
+
+struct percpu_swap_cluster {
+	struct swap_info_struct *si[SWAP_NR_ORDERS];
+	unsigned long offset[SWAP_NR_ORDERS];
+	local_lock_t lock;
+};
+
+static DEFINE_PER_CPU(struct percpu_swap_cluster, percpu_swap_cluster) = {
+	.si = { NULL },
+	.offset = { SWAP_ENTRY_INVALID },
+	.lock = INIT_LOCAL_LOCK(),
+};
+
+/* May return NULL on invalid type, caller must check for NULL return */
+static struct swap_info_struct *swap_type_to_info(int type)
+{
+	if (type < 0 || type >= MAX_SWAPFILES)
+		return NULL;
+	return READ_ONCE(swap_info[type]); /* rcu_dereference() */
+}
+
+/* May return NULL on invalid entry, caller must check for NULL return */
+static struct swap_info_struct *swap_entry_to_info(swp_entry_t entry)
+{
+	return swap_type_to_info(swp_type(entry));
+}
+
+/*
+ * Use the second highest bit of inuse_pages counter as the indicator
+ * if one swap device is on the available plist, so the atomic can
+ * still be updated arithmetically while having special data embedded.
+ *
+ * inuse_pages counter is the only thing indicating if a device should
+ * be on avail_lists or not (except swapon / swapoff). By embedding the
+ * off-list bit in the atomic counter, updates no longer need any lock
+ * to check the list status.
+ *
+ * This bit will be set if the device is not on the plist and not
+ * usable, will be cleared if the device is on the plist.
+ */
+#define SWAP_USAGE_OFFLIST_BIT (1UL << (BITS_PER_TYPE(atomic_long_t) - 2))
+#define SWAP_USAGE_COUNTER_MASK (~SWAP_USAGE_OFFLIST_BIT)
+static long swap_usage_in_pages(struct swap_info_struct *si)
+{
+	return atomic_long_read(&si->inuse_pages) & SWAP_USAGE_COUNTER_MASK;
+}
+
+/* Reclaim the swap entry anyway if possible */
+#define TTRS_ANYWAY		0x1
+/*
+ * Reclaim the swap entry if there are no more mappings of the
+ * corresponding page
+ */
+#define TTRS_UNMAPPED		0x2
+/* Reclaim the swap entry if swap is getting full */
+#define TTRS_FULL		0x4
+
+static bool swap_only_has_cache(struct swap_cluster_info *ci,
+				unsigned long offset, int nr_pages)
+{
+	unsigned int ci_off = offset % SWAPFILE_CLUSTER;
+	unsigned int ci_end = ci_off + nr_pages;
+	unsigned long swp_tb;
+
+	do {
+		swp_tb = __swap_table_get(ci, ci_off);
+		VM_WARN_ON_ONCE(!swp_tb_is_folio(swp_tb));
+		if (swp_tb_get_count(swp_tb))
+			return false;
+	} while (++ci_off < ci_end);
+
+	return true;
+}
+
+/*
+ * returns number of pages in the folio that backs the swap entry. If positive,
+ * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no
+ * folio was associated with the swap entry.
+ */
+static int __try_to_reclaim_swap(struct swap_info_struct *si,
+				 unsigned long offset, unsigned long flags)
+{
+	const swp_entry_t entry = swp_entry(si->type, offset);
+	struct swap_cluster_info *ci;
+	struct folio *folio;
+	int ret, nr_pages;
+	bool need_reclaim;
+
+again:
+	folio = swap_cache_get_folio(entry);
+	if (!folio)
+		return 0;
+
+	nr_pages = folio_nr_pages(folio);
+	ret = -nr_pages;
+
+	/*
+	 * We hold a folio lock here. We have to use trylock for
+	 * avoiding deadlock. This is a special case and you should
+	 * use folio_free_swap() with explicit folio_lock() in usual
+	 * operations.
+	 */
+	if (!folio_trylock(folio))
+		goto out;
+
+	/*
+	 * Offset could point to the middle of a large folio, or folio
+	 * may no longer point to the expected offset before it's locked.
+	 */
+	if (!folio_matches_swap_entry(folio, entry)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		goto again;
+	}
+	offset = swp_offset(folio->swap);
+
+	need_reclaim = ((flags & TTRS_ANYWAY) ||
+			((flags & TTRS_UNMAPPED) && !folio_mapped(folio)) ||
+			((flags & TTRS_FULL) && mem_cgroup_swap_full(folio)));
+	if (!need_reclaim || !folio_swapcache_freeable(folio))
+		goto out_unlock;
+
+	/*
+	 * It's safe to delete the folio from swap cache only if the folio
+	 * is in swap cache with swap count == 0. The slots have no page table
+	 * reference or pending writeback, and can't be allocated to others.
+	 */
+	ci = swap_cluster_lock(si, offset);
+	need_reclaim = swap_only_has_cache(ci, offset, nr_pages);
+	swap_cluster_unlock(ci);
+	if (!need_reclaim)
+		goto out_unlock;
+
+	swap_cache_del_folio(folio);
+	folio_set_dirty(folio);
+	ret = nr_pages;
+out_unlock:
+	folio_unlock(folio);
+out:
+	folio_put(folio);
+	return ret;
+}
+
+static inline struct swap_extent *first_se(struct swap_info_struct *sis)
+{
+	struct rb_node *rb = rb_first(&sis->swap_extent_root);
+	return rb_entry(rb, struct swap_extent, rb_node);
+}
+
+static inline struct swap_extent *next_se(struct swap_extent *se)
+{
+	struct rb_node *rb = rb_next(&se->rb_node);
+	return rb ? rb_entry(rb, struct swap_extent, rb_node) : NULL;
+}
+
+/*
+ * swapon tell device that all the old swap contents can be discarded,
+ * to allow the swap device to optimize its wear-levelling.
+ */
+static int discard_swap(struct swap_info_struct *si)
+{
+	struct swap_extent *se;
+	sector_t start_block;
+	sector_t nr_blocks;
+	int err = 0;
+
+	/* Do not discard the swap header page! */
+	se = first_se(si);
+	start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
+	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
+	if (nr_blocks) {
+		err = blkdev_issue_discard(si->bdev, start_block,
+				nr_blocks, GFP_KERNEL);
+		if (err)
+			return err;
+		cond_resched();
+	}
+
+	for (se = next_se(se); se; se = next_se(se)) {
+		start_block = se->start_block << (PAGE_SHIFT - 9);
+		nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
+
+		err = blkdev_issue_discard(si->bdev, start_block,
+				nr_blocks, GFP_KERNEL);
+		if (err)
+			break;
+
+		cond_resched();
+	}
+	return err;		/* That will often be -EOPNOTSUPP */
+}
+
+static struct swap_extent *
+offset_to_swap_extent(struct swap_info_struct *sis, unsigned long offset)
+{
+	struct swap_extent *se;
+	struct rb_node *rb;
+
+	rb = sis->swap_extent_root.rb_node;
+	while (rb) {
+		se = rb_entry(rb, struct swap_extent, rb_node);
+		if (offset < se->start_page)
+			rb = rb->rb_left;
+		else if (offset >= se->start_page + se->nr_pages)
+			rb = rb->rb_right;
+		else
+			return se;
+	}
+	/* It *must* be present */
+	BUG();
+}
+
+sector_t swap_folio_sector(struct folio *folio)
+{
+	struct swap_info_struct *sis = __swap_entry_to_info(folio->swap);
+	struct swap_extent *se;
+	sector_t sector;
+	pgoff_t offset;
+
+	offset = swp_offset(folio->swap);
+	se = offset_to_swap_extent(sis, offset);
+	sector = se->start_block + (offset - se->start_page);
+	return sector << (PAGE_SHIFT - 9);
+}
+
+/*
+ * swap allocation tell device that a cluster of swap can now be discarded,
+ * to allow the swap device to optimize its wear-levelling.
+ */
+static void discard_swap_cluster(struct swap_info_struct *si,
+				 pgoff_t start_page, pgoff_t nr_pages)
+{
+	struct swap_extent *se = offset_to_swap_extent(si, start_page);
+
+	while (nr_pages) {
+		pgoff_t offset = start_page - se->start_page;
+		sector_t start_block = se->start_block + offset;
+		sector_t nr_blocks = se->nr_pages - offset;
+
+		if (nr_blocks > nr_pages)
+			nr_blocks = nr_pages;
+		start_page += nr_blocks;
+		nr_pages -= nr_blocks;
+
+		start_block <<= PAGE_SHIFT - 9;
+		nr_blocks <<= PAGE_SHIFT - 9;
+		if (blkdev_issue_discard(si->bdev, start_block,
+					nr_blocks, GFP_NOIO))
+			break;
+
+		se = next_se(se);
+	}
+}
+
+#define LATENCY_LIMIT		256
+
+static inline bool cluster_is_empty(struct swap_cluster_info *info)
+{
+	return info->count == 0;
+}
+
+static inline bool cluster_is_discard(struct swap_cluster_info *info)
+{
+	return info->flags == CLUSTER_FLAG_DISCARD;
+}
+
+static inline bool cluster_table_is_alloced(struct swap_cluster_info *ci)
+{
+	return rcu_dereference_protected(ci->table, lockdep_is_held(&ci->lock));
+}
+
+static inline bool cluster_is_usable(struct swap_cluster_info *ci, int order)
+{
+	if (unlikely(ci->flags > CLUSTER_FLAG_USABLE))
+		return false;
+	if (!cluster_table_is_alloced(ci))
+		return false;
+	if (!order)
+		return true;
+	return cluster_is_empty(ci) || order == ci->order;
+}
+
+static inline unsigned int cluster_index(struct swap_info_struct *si,
+					 struct swap_cluster_info *ci)
+{
+	return ci - si->cluster_info;
+}
+
+static inline unsigned int cluster_offset(struct swap_info_struct *si,
+					  struct swap_cluster_info *ci)
+{
+	return cluster_index(si, ci) * SWAPFILE_CLUSTER;
+}
+
+static void swap_cluster_free_table_folio_rcu_cb(struct rcu_head *head)
+{
+	struct folio *folio;
+
+	folio = page_folio(container_of(head, struct page, rcu_head));
+	folio_put(folio);
+}
+
+static void swap_cluster_free_table(struct swap_cluster_info *ci)
+{
+	struct swap_table *table;
+
+#ifdef CONFIG_MEMCG
+	kfree(ci->memcg_table);
+	ci->memcg_table = NULL;
+#endif
+
+#if !SWAP_TABLE_HAS_ZEROFLAG
+	kfree(ci->zero_bitmap);
+	ci->zero_bitmap = NULL;
+#endif
+
+	table = (struct swap_table *)rcu_access_pointer(ci->table);
+	if (!table)
+		return;
+
+	rcu_assign_pointer(ci->table, NULL);
+	if (!SWP_TABLE_USE_PAGE) {
+		kmem_cache_free(swap_table_cachep, table);
+		return;
+	}
+
+	call_rcu(&(folio_page(virt_to_folio(table), 0)->rcu_head),
+		 swap_cluster_free_table_folio_rcu_cb);
+}
+
+static int swap_cluster_alloc_table(struct swap_cluster_info *ci, gfp_t gfp)
+{
+	struct swap_table *table = NULL;
+	struct folio *folio;
+
+	/* The cluster must be empty and not on any list during allocation. */
+	VM_WARN_ON_ONCE(ci->flags || !cluster_is_empty(ci));
+	if (rcu_access_pointer(ci->table))
+		return 0;
+
+	if (SWP_TABLE_USE_PAGE) {
+		folio = folio_alloc(gfp | __GFP_ZERO, 0);
+		if (folio)
+			table = folio_address(folio);
+	} else {
+		table = kmem_cache_zalloc(swap_table_cachep, gfp);
+	}
+	if (!table)
+		return -ENOMEM;
+
+	rcu_assign_pointer(ci->table, table);
+
+#ifdef CONFIG_MEMCG
+	if (!mem_cgroup_disabled()) {
+		VM_WARN_ON_ONCE(ci->memcg_table);
+		ci->memcg_table = kzalloc_obj(*ci->memcg_table, gfp);
+		if (!ci->memcg_table) {
+			swap_cluster_free_table(ci);
+			return -ENOMEM;
+		}
+	}
+#endif
+
+#if !SWAP_TABLE_HAS_ZEROFLAG
+	VM_WARN_ON_ONCE(ci->zero_bitmap);
+	ci->zero_bitmap = bitmap_zalloc(SWAPFILE_CLUSTER, gfp);
+	if (!ci->zero_bitmap) {
+		swap_cluster_free_table(ci);
+		return -ENOMEM;
+	}
+#endif
+	return 0;
+}
+
+/*
+ * Sanity check to ensure nothing leaked, and the specified range is empty.
+ * One special case is that bad slots can't be freed, so check the number of
+ * bad slots for swapoff, and non-swapoff path must never free bad slots.
+ */
+static void swap_cluster_assert_empty(struct swap_cluster_info *ci,
+				      unsigned int ci_off, unsigned int nr,
+				      bool swapoff)
+{
+	unsigned int ci_end = ci_off + nr;
+	unsigned long swp_tb;
+	int bad_slots = 0;
+
+	if (!IS_ENABLED(CONFIG_DEBUG_VM) && !swapoff)
+		return;
+
+	do {
+		swp_tb = __swap_table_get(ci, ci_off);
+		if (swp_tb_is_bad(swp_tb))
+			bad_slots++;
+		else
+			WARN_ON_ONCE(!swp_tb_is_null(swp_tb));
+		WARN_ON_ONCE(__swap_cgroup_get(ci, ci_off));
+	} while (++ci_off < ci_end);
+
+	WARN_ON_ONCE(bad_slots != (swapoff ? ci->count : 0));
+	WARN_ON_ONCE(nr == SWAPFILE_CLUSTER && ci->extend_table);
+}
+
+/*
+ * Allocate swap table for one cluster. Attempt an atomic allocation first,
+ * then fallback to sleeping allocation.
+ */
+static struct swap_cluster_info *
+swap_cluster_populate(struct swap_info_struct *si,
+			 struct swap_cluster_info *ci)
+{
+	int ret;
+
+	/*
+	 * Only cluster isolation from the allocator does table allocation.
+	 * Swap allocator uses percpu clusters and holds the local lock.
+	 */
+	lockdep_assert_held(&this_cpu_ptr(&percpu_swap_cluster)->lock);
+	if (!(si->flags & SWP_SOLIDSTATE))
+		lockdep_assert_held(&si->global_cluster_lock);
+	lockdep_assert_held(&ci->lock);
+
+	if (!swap_cluster_alloc_table(ci, __GFP_HIGH | __GFP_NOMEMALLOC |
+					  __GFP_NOWARN))
+		return ci;
+
+	/*
+	 * Try a sleep allocation. Each isolated free cluster may cause
+	 * a sleep allocation, but there is a limited number of them, so
+	 * the potential recursive allocation is limited.
+	 */
+	spin_unlock(&ci->lock);
+	if (!(si->flags & SWP_SOLIDSTATE))
+		spin_unlock(&si->global_cluster_lock);
+	local_unlock(&percpu_swap_cluster.lock);
+
+	ret = swap_cluster_alloc_table(ci, __GFP_HIGH | __GFP_NOMEMALLOC |
+					   GFP_KERNEL);
+
+	/*
+	 * Back to atomic context. We might have migrated to a new CPU with a
+	 * usable percpu cluster. But just keep using the isolated cluster to
+	 * make things easier. Migration indicates a slight change of workload
+	 * so using a new free cluster might not be a bad idea, and the worst
+	 * could happen with ignoring the percpu cluster is fragmentation,
+	 * which is acceptable since this fallback and race is rare.
+	 */
+	local_lock(&percpu_swap_cluster.lock);
+	if (!(si->flags & SWP_SOLIDSTATE))
+		spin_lock(&si->global_cluster_lock);
+	spin_lock(&ci->lock);
+
+	if (ret) {
+		move_cluster(si, ci, &si->free_clusters, CLUSTER_FLAG_FREE);
+		spin_unlock(&ci->lock);
+		return NULL;
+	}
+	return ci;
+}
+
+static void move_cluster(struct swap_info_struct *si,
+			 struct swap_cluster_info *ci, struct list_head *list,
+			 enum swap_cluster_flags new_flags)
+{
+	VM_WARN_ON(ci->flags == new_flags);
+
+	BUILD_BUG_ON(1 << sizeof(ci->flags) * BITS_PER_BYTE < CLUSTER_FLAG_MAX);
+	lockdep_assert_held(&ci->lock);
+
+	spin_lock(&si->lock);
+	if (ci->flags == CLUSTER_FLAG_NONE)
+		list_add_tail(&ci->list, list);
+	else
+		list_move_tail(&ci->list, list);
+	spin_unlock(&si->lock);
+	ci->flags = new_flags;
+}
+
+/* Add a cluster to discard list and schedule it to do discard */
+static void swap_cluster_schedule_discard(struct swap_info_struct *si,
+		struct swap_cluster_info *ci)
+{
+	VM_BUG_ON(ci->flags == CLUSTER_FLAG_FREE);
+	move_cluster(si, ci, &si->discard_clusters, CLUSTER_FLAG_DISCARD);
+	schedule_work(&si->discard_work);
+}
+
+static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
+{
+	swap_cluster_assert_empty(ci, 0, SWAPFILE_CLUSTER, false);
+	swap_cluster_free_table(ci);
+	move_cluster(si, ci, &si->free_clusters, CLUSTER_FLAG_FREE);
+	ci->order = 0;
+}
+
+/*
+ * Isolate and lock the first cluster that is not contented on a list,
+ * clean its flag before taken off-list. Cluster flag must be in sync
+ * with list status, so cluster updaters can always know the cluster
+ * list status without touching si lock.
+ *
+ * Note it's possible that all clusters on a list are contented so
+ * this returns NULL for an non-empty list.
+ */
+static struct swap_cluster_info *isolate_lock_cluster(
+		struct swap_info_struct *si, struct list_head *list)
+{
+	struct swap_cluster_info *ci, *found = NULL;
+	u8 flags = CLUSTER_FLAG_NONE;
+
+	spin_lock(&si->lock);
+	list_for_each_entry(ci, list, list) {
+		if (!spin_trylock(&ci->lock))
+			continue;
+
+		/* We may only isolate and clear flags of following lists */
+		VM_BUG_ON(!ci->flags);
+		VM_BUG_ON(ci->flags > CLUSTER_FLAG_USABLE &&
+			  ci->flags != CLUSTER_FLAG_FULL);
+
+		list_del(&ci->list);
+		flags = ci->flags;
+		ci->flags = CLUSTER_FLAG_NONE;
+		found = ci;
+		break;
+	}
+	spin_unlock(&si->lock);
+
+	/* Cluster's table is freed when and only when it's on the free list. */
+	if (found && flags == CLUSTER_FLAG_FREE) {
+		VM_WARN_ON_ONCE(list != &si->free_clusters);
+		VM_WARN_ON_ONCE(cluster_table_is_alloced(found));
+		return swap_cluster_populate(si, found);
+	}
+
+	return found;
+}
+
+/*
+ * Doing discard actually. After a cluster discard is finished, the cluster
+ * will be added to free cluster list. Discard cluster is a bit special as
+ * they don't participate in allocation or reclaim, so clusters marked as
+ * CLUSTER_FLAG_DISCARD must remain off-list or on discard list.
+ */
+static bool swap_do_scheduled_discard(struct swap_info_struct *si)
+{
+	struct swap_cluster_info *ci;
+	bool ret = false;
+	unsigned int idx;
+
+	spin_lock(&si->lock);
+	while (!list_empty(&si->discard_clusters)) {
+		ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
+		/*
+		 * Delete the cluster from list to prepare for discard, but keep
+		 * the CLUSTER_FLAG_DISCARD flag, percpu_swap_cluster could be
+		 * pointing to it, or ran into by relocate_cluster.
+		 */
+		list_del(&ci->list);
+		idx = cluster_index(si, ci);
+		spin_unlock(&si->lock);
+		discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
+				SWAPFILE_CLUSTER);
+
+		spin_lock(&ci->lock);
+		/*
+		 * Discard is done, clear its flags as it's off-list, then
+		 * return the cluster to allocation list.
+		 */
+		ci->flags = CLUSTER_FLAG_NONE;
+		__free_cluster(si, ci);
+		spin_unlock(&ci->lock);
+		ret = true;
+		spin_lock(&si->lock);
+	}
+	spin_unlock(&si->lock);
+	return ret;
+}
+
+static void swap_discard_work(struct work_struct *work)
+{
+	struct swap_info_struct *si;
+
+	si = container_of(work, struct swap_info_struct, discard_work);
+
+	swap_do_scheduled_discard(si);
+}
+
+static void swap_users_ref_free(struct percpu_ref *ref)
+{
+	struct swap_info_struct *si;
+
+	si = container_of(ref, struct swap_info_struct, users);
+	complete(&si->comp);
+}
+
+/*
+ * Must be called after freeing if ci->count == 0, moves the cluster to free
+ * or discard list.
+ */
+static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
+{
+	VM_BUG_ON(ci->count != 0);
+	VM_BUG_ON(ci->flags == CLUSTER_FLAG_FREE);
+	lockdep_assert_held(&ci->lock);
+
+	/*
+	 * If the swap is discardable, prepare discard the cluster
+	 * instead of free it immediately. The cluster will be freed
+	 * after discard.
+	 */
+	if ((si->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
+	    (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
+		swap_cluster_schedule_discard(si, ci);
+		return;
+	}
+
+	__free_cluster(si, ci);
+}
+
+/*
+ * Must be called after freeing if ci->count != 0, moves the cluster to
+ * nonfull list.
+ */
+static void partial_free_cluster(struct swap_info_struct *si,
+				 struct swap_cluster_info *ci)
+{
+	VM_BUG_ON(!ci->count || ci->count == SWAPFILE_CLUSTER);
+	lockdep_assert_held(&ci->lock);
+
+	if (ci->flags != CLUSTER_FLAG_NONFULL)
+		move_cluster(si, ci, &si->nonfull_clusters[ci->order],
+			     CLUSTER_FLAG_NONFULL);
+}
+
+/*
+ * Must be called after allocation, moves the cluster to full or frag list.
+ * Note: allocation doesn't acquire si lock, and may drop the ci lock for
+ * reclaim, so the cluster could be any where when called.
+ */
+static void relocate_cluster(struct swap_info_struct *si,
+			     struct swap_cluster_info *ci)
+{
+	lockdep_assert_held(&ci->lock);
+
+	/* Discard cluster must remain off-list or on discard list */
+	if (cluster_is_discard(ci))
+		return;
+
+	if (!ci->count) {
+		if (ci->flags != CLUSTER_FLAG_FREE)
+			free_cluster(si, ci);
+	} else if (ci->count != SWAPFILE_CLUSTER) {
+		if (ci->flags != CLUSTER_FLAG_FRAG)
+			move_cluster(si, ci, &si->frag_clusters[ci->order],
+				     CLUSTER_FLAG_FRAG);
+	} else {
+		if (ci->flags != CLUSTER_FLAG_FULL)
+			move_cluster(si, ci, &si->full_clusters,
+				     CLUSTER_FLAG_FULL);
+	}
+}
+
+/*
+ * The cluster corresponding to @offset will be accounted as having one bad
+ * slot. The cluster will not be added to the free cluster list, and its
+ * usage counter will be increased by 1. Only used for initialization.
+ */
+static int swap_cluster_setup_bad_slot(struct swap_info_struct *si,
+				       struct swap_cluster_info *cluster_info,
+				       unsigned int offset, bool mask)
+{
+	unsigned int ci_off = offset % SWAPFILE_CLUSTER;
+	unsigned long idx = offset / SWAPFILE_CLUSTER;
+	struct swap_cluster_info *ci;
+	int ret = 0;
+
+	/* si->max may got shrunk by swap swap_activate() */
+	if (offset >= si->max && !mask) {
+		pr_debug("Ignoring bad slot %u (max: %u)\n", offset, si->max);
+		return 0;
+	}
+	/*
+	 * Account it, skip header slot: si->pages is initiated as
+	 * si->max - 1. Also skip the masking of last cluster,
+	 * si->pages doesn't include that part.
+	 */
+	if (offset && !mask)
+		si->pages -= 1;
+	if (!si->pages) {
+		pr_warn("Empty swap-file\n");
+		return -EINVAL;
+	}
+
+	ci = cluster_info + idx;
+	/* Need to allocate swap table first for initial bad slot marking. */
+	if (!ci->count && swap_cluster_alloc_table(ci, GFP_KERNEL))
+		return -ENOMEM;
+	spin_lock(&ci->lock);
+	/* Check for duplicated bad swap slots. */
+	if (__swap_table_xchg(ci, ci_off, SWP_TB_BAD) != SWP_TB_NULL) {
+		pr_warn("Duplicated bad slot offset %d\n", offset);
+		ret = -EINVAL;
+	} else {
+		ci->count++;
+	}
+	spin_unlock(&ci->lock);
+
+	WARN_ON(ci->count > SWAPFILE_CLUSTER);
+	WARN_ON(ci->flags);
+
+	return ret;
+}
+
+/*
+ * Reclaim drops the ci lock, so the cluster may become unusable (freed or
+ * stolen by a lower order). @usable will be set to false if that happens.
+ */
+static bool cluster_reclaim_range(struct swap_info_struct *si,
+				  struct swap_cluster_info *ci,
+				  unsigned long start, unsigned int order,
+				  bool *usable)
+{
+	unsigned int nr_pages = 1 << order;
+	unsigned long offset = start, end = start + nr_pages;
+	unsigned long swp_tb;
+
+	spin_unlock(&ci->lock);
+	do {
+		swp_tb = swap_table_get(ci, offset % SWAPFILE_CLUSTER);
+		if (swp_tb_get_count(swp_tb))
+			break;
+		if (swp_tb_is_folio(swp_tb))
+			if (__try_to_reclaim_swap(si, offset, TTRS_ANYWAY) < 0)
+				break;
+	} while (++offset < end);
+	spin_lock(&ci->lock);
+
+	/*
+	 * We just dropped ci->lock so cluster could be used by another
+	 * order or got freed, check if it's still usable or empty.
+	 */
+	if (!cluster_is_usable(ci, order)) {
+		*usable = false;
+		return false;
+	}
+	*usable = true;
+
+	/* Fast path, no need to scan if the whole cluster is empty */
+	if (cluster_is_empty(ci))
+		return true;
+
+	/*
+	 * Recheck the range no matter reclaim succeeded or not, the slot
+	 * could have been be freed while we are not holding the lock.
+	 */
+	for (offset = start; offset < end; offset++) {
+		swp_tb = __swap_table_get(ci, offset % SWAPFILE_CLUSTER);
+		if (!swp_tb_is_null(swp_tb))
+			return false;
+	}
+
+	return true;
+}
+
+static bool cluster_scan_range(struct swap_info_struct *si,
+			       struct swap_cluster_info *ci,
+			       unsigned long offset, unsigned int nr_pages,
+			       bool *need_reclaim)
+{
+	unsigned int ci_off = offset % SWAPFILE_CLUSTER;
+	unsigned int ci_end = ci_off + nr_pages;
+	unsigned long swp_tb;
+
+	do {
+		swp_tb = __swap_table_get(ci, ci_off);
+		if (swp_tb_is_null(swp_tb))
+			continue;
+		if (swp_tb_is_folio(swp_tb) && !__swp_tb_get_count(swp_tb)) {
+			if (!vm_swap_full())
+				return false;
+			*need_reclaim = true;
+			continue;
+		}
+		/* Slot with zero count can only be NULL or folio */
+		VM_WARN_ON(!swp_tb_get_count(swp_tb));
+		return false;
+	} while (++ci_off < ci_end);
+
+	return true;
+}
+
+static bool __swap_cluster_alloc_entries(struct swap_info_struct *si,
+					 struct swap_cluster_info *ci,
+					 struct folio *folio,
+					 unsigned int ci_off)
+{
+	unsigned int order;
+	unsigned long nr_pages;
+
+	lockdep_assert_held(&ci->lock);
+
+	if (!(si->flags & SWP_WRITEOK))
+		return false;
+
+	/*
+	 * All mm swap allocation starts with a folio (folio_alloc_swap),
+	 * it's also the only allocation path for large orders allocation.
+	 * Such swap slots starts with count == 0 and will be increased
+	 * upon folio unmap.
+	 *
+	 * Else, it's a exclusive order 0 allocation for hibernation.
+	 * The slot starts with count == 1 and never increases.
+	 */
+	if (likely(folio)) {
+		order = folio_order(folio);
+		nr_pages = 1 << order;
+		swap_cluster_assert_empty(ci, ci_off, nr_pages, false);
+		__swap_cache_add_folio(ci, folio, swp_entry(si->type,
+							    ci_off + cluster_offset(si, ci)));
+	} else if (IS_ENABLED(CONFIG_HIBERNATION)) {
+		order = 0;
+		nr_pages = 1;
+		swap_cluster_assert_empty(ci, ci_off, 1, false);
+		/* Fake shadow placeholder with no flag, hibernation does not use the zeromap */
+		__swap_table_set(ci, ci_off, __swp_tb_mk_count(shadow_to_swp_tb(NULL, 0), 1));
+	} else {
+		/* Allocation without folio is only possible with hibernation */
+		WARN_ON_ONCE(1);
+		return false;
+	}
+
+	/*
+	 * The first allocation in a cluster makes the
+	 * cluster exclusive to this order
+	 */
+	if (cluster_is_empty(ci))
+		ci->order = order;
+	ci->count += nr_pages;
+	swap_range_alloc(si, nr_pages);
+
+	return true;
+}
+
+/* Try use a new cluster for current CPU and allocate from it. */
+static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
+					    struct swap_cluster_info *ci,
+					    struct folio *folio, unsigned long offset)
+{
+	unsigned int next = SWAP_ENTRY_INVALID, found = SWAP_ENTRY_INVALID;
+	unsigned long start = ALIGN_DOWN(offset, SWAPFILE_CLUSTER);
+	unsigned int order = likely(folio) ? folio_order(folio) : 0;
+	unsigned long end = start + SWAPFILE_CLUSTER;
+	unsigned int nr_pages = 1 << order;
+	bool need_reclaim, ret, usable;
+
+	lockdep_assert_held(&ci->lock);
+	VM_WARN_ON(!cluster_is_usable(ci, order));
+
+	if (end < nr_pages || ci->count + nr_pages > SWAPFILE_CLUSTER)
+		goto out;
+
+	for (end -= nr_pages; offset <= end; offset += nr_pages) {
+		need_reclaim = false;
+		if (!cluster_scan_range(si, ci, offset, nr_pages, &need_reclaim))
+			continue;
+		if (need_reclaim) {
+			ret = cluster_reclaim_range(si, ci, offset, order, &usable);
+			if (!usable)
+				goto out;
+			if (cluster_is_empty(ci))
+				offset = start;
+			/* Reclaim failed but cluster is usable, try next */
+			if (!ret)
+				continue;
+		}
+		if (!__swap_cluster_alloc_entries(si, ci, folio, offset % SWAPFILE_CLUSTER))
+			break;
+		found = offset;
+		offset += nr_pages;
+		if (ci->count < SWAPFILE_CLUSTER && offset <= end)
+			next = offset;
+		break;
+	}
+out:
+	relocate_cluster(si, ci);
+	swap_cluster_unlock(ci);
+	if (si->flags & SWP_SOLIDSTATE) {
+		this_cpu_write(percpu_swap_cluster.offset[order], next);
+		this_cpu_write(percpu_swap_cluster.si[order], si);
+	} else {
+		si->global_cluster->next[order] = next;
+	}
+	return found;
+}
+
+static unsigned int alloc_swap_scan_list(struct swap_info_struct *si,
+					 struct list_head *list,
+					 struct folio *folio,
+					 bool scan_all)
+{
+	unsigned int found = SWAP_ENTRY_INVALID;
+
+	do {
+		struct swap_cluster_info *ci = isolate_lock_cluster(si, list);
+		unsigned long offset;
+
+		if (!ci)
+			break;
+		offset = cluster_offset(si, ci);
+		found = alloc_swap_scan_cluster(si, ci, folio, offset);
+		if (found)
+			break;
+	} while (scan_all);
+
+	return found;
+}
+
+static void swap_reclaim_full_clusters(struct swap_info_struct *si, bool force)
+{
+	long to_scan = 1;
+	unsigned long offset, end;
+	struct swap_cluster_info *ci;
+	unsigned long swp_tb;
+	int nr_reclaim;
+
+	if (force)
+		to_scan = swap_usage_in_pages(si) / SWAPFILE_CLUSTER;
+
+	while ((ci = isolate_lock_cluster(si, &si->full_clusters))) {
+		offset = cluster_offset(si, ci);
+		end = min(si->max, offset + SWAPFILE_CLUSTER);
+		to_scan--;
+
+		while (offset < end) {
+			swp_tb = swap_table_get(ci, offset % SWAPFILE_CLUSTER);
+			if (swp_tb_is_folio(swp_tb) && !__swp_tb_get_count(swp_tb)) {
+				spin_unlock(&ci->lock);
+				nr_reclaim = __try_to_reclaim_swap(si, offset,
+								   TTRS_ANYWAY);
+				spin_lock(&ci->lock);
+				if (nr_reclaim) {
+					offset += abs(nr_reclaim);
+					continue;
+				}
+			}
+			offset++;
+		}
+
+		/* in case no swap cache is reclaimed */
+		if (ci->flags == CLUSTER_FLAG_NONE)
+			relocate_cluster(si, ci);
+
+		swap_cluster_unlock(ci);
+		if (to_scan <= 0)
+			break;
+
+		/*
+		 * When 'force' is false, 'to_scan' is initialized to 1.
+		 * The loop breaks above, making this cond_resched() unreachable
+		 * in atomic contexts.
+		 */
+		cond_resched();
+	}
+}
+
+static void swap_reclaim_work(struct work_struct *work)
+{
+	struct swap_info_struct *si;
+
+	si = container_of(work, struct swap_info_struct, reclaim_work);
+
+	swap_reclaim_full_clusters(si, true);
+}
+
+/*
+ * Try to allocate swap entries with specified order and try set a new
+ * cluster for current CPU too.
+ */
+static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si,
+					      struct folio *folio)
+{
+	struct swap_cluster_info *ci;
+	unsigned int order = likely(folio) ? folio_order(folio) : 0;
+	unsigned int offset = SWAP_ENTRY_INVALID, found = SWAP_ENTRY_INVALID;
+
+	/*
+	 * Swapfile is not block device so unable
+	 * to allocate large entries.
+	 */
+	if (order && !(si->flags & SWP_BLKDEV))
+		return 0;
+
+	if (!(si->flags & SWP_SOLIDSTATE)) {
+		/* Serialize HDD SWAP allocation for each device. */
+		spin_lock(&si->global_cluster_lock);
+		offset = si->global_cluster->next[order];
+		if (offset == SWAP_ENTRY_INVALID)
+			goto new_cluster;
+
+		ci = swap_cluster_lock(si, offset);
+		/* Cluster could have been used by another order */
+		if (cluster_is_usable(ci, order)) {
+			if (cluster_is_empty(ci))
+				offset = cluster_offset(si, ci);
+			found = alloc_swap_scan_cluster(si, ci, folio, offset);
+		} else {
+			swap_cluster_unlock(ci);
+		}
+		if (found)
+			goto done;
+	}
+
+new_cluster:
+	/*
+	 * If the device need discard, prefer new cluster over nonfull
+	 * to spread out the writes.
+	 */
+	if (si->flags & SWP_PAGE_DISCARD) {
+		found = alloc_swap_scan_list(si, &si->free_clusters, folio, false);
+		if (found)
+			goto done;
+	}
+
+	if (order < PMD_ORDER) {
+		found = alloc_swap_scan_list(si, &si->nonfull_clusters[order], folio, true);
+		if (found)
+			goto done;
+	}
+
+	if (!(si->flags & SWP_PAGE_DISCARD)) {
+		found = alloc_swap_scan_list(si, &si->free_clusters, folio, false);
+		if (found)
+			goto done;
+	}
+
+	/* Try reclaim full clusters if free and nonfull lists are drained */
+	if (vm_swap_full())
+		swap_reclaim_full_clusters(si, false);
+
+	if (order < PMD_ORDER) {
+		/*
+		 * Scan only one fragment cluster is good enough. Order 0
+		 * allocation will surely success, and large allocation
+		 * failure is not critical. Scanning one cluster still
+		 * keeps the list rotated and reclaimed (for clean swap cache).
+		 */
+		found = alloc_swap_scan_list(si, &si->frag_clusters[order], folio, false);
+		if (found)
+			goto done;
+	}
+
+	if (order)
+		goto done;
+
+	/* Order 0 stealing from higher order */
+	for (int o = 1; o < SWAP_NR_ORDERS; o++) {
+		/*
+		 * Clusters here have at least one usable slots and can't fail order 0
+		 * allocation, but reclaim may drop si->lock and race with another user.
+		 */
+		found = alloc_swap_scan_list(si, &si->frag_clusters[o], folio, true);
+		if (found)
+			goto done;
+
+		found = alloc_swap_scan_list(si, &si->nonfull_clusters[o], folio, true);
+		if (found)
+			goto done;
+	}
+done:
+	if (!(si->flags & SWP_SOLIDSTATE))
+		spin_unlock(&si->global_cluster_lock);
+
+	return found;
+}
+
+/* SWAP_USAGE_OFFLIST_BIT can only be set by this helper. */
+static void del_from_avail_list(struct swap_info_struct *si, bool swapoff)
+{
+	unsigned long pages;
+
+	spin_lock(&swap_avail_lock);
+
+	if (swapoff) {
+		/*
+		 * Forcefully remove it. Clear the SWP_WRITEOK flags for
+		 * swapoff here so it's synchronized by both si->lock and
+		 * swap_avail_lock, to ensure the result can be seen by
+		 * add_to_avail_list.
+		 */
+		lockdep_assert_held(&si->lock);
+		si->flags &= ~SWP_WRITEOK;
+		atomic_long_or(SWAP_USAGE_OFFLIST_BIT, &si->inuse_pages);
+	} else {
+		/*
+		 * If not called by swapoff, take it off-list only if it's
+		 * full and SWAP_USAGE_OFFLIST_BIT is not set (strictly
+		 * si->inuse_pages == pages), any concurrent slot freeing,
+		 * or device already removed from plist by someone else
+		 * will make this return false.
+		 */
+		pages = si->pages;
+		if (!atomic_long_try_cmpxchg(&si->inuse_pages, &pages,
+					     pages | SWAP_USAGE_OFFLIST_BIT))
+			goto skip;
+	}
+
+	plist_del(&si->avail_list, &swap_avail_head);
+
+skip:
+	spin_unlock(&swap_avail_lock);
+}
+
+/* SWAP_USAGE_OFFLIST_BIT can only be cleared by this helper. */
+static void add_to_avail_list(struct swap_info_struct *si, bool swapon)
+{
+	long val;
+	unsigned long pages;
+
+	spin_lock(&swap_avail_lock);
+
+	/* Corresponding to SWP_WRITEOK clearing in del_from_avail_list */
+	if (swapon) {
+		lockdep_assert_held(&si->lock);
+		si->flags |= SWP_WRITEOK;
+	} else {
+		if (!(READ_ONCE(si->flags) & SWP_WRITEOK))
+			goto skip;
+	}
+
+	if (!(atomic_long_read(&si->inuse_pages) & SWAP_USAGE_OFFLIST_BIT))
+		goto skip;
+
+	val = atomic_long_fetch_and_relaxed(~SWAP_USAGE_OFFLIST_BIT, &si->inuse_pages);
+
+	/*
+	 * When device is full and device is on the plist, only one updater will
+	 * see (inuse_pages == si->pages) and will call del_from_avail_list. If
+	 * that updater happen to be here, just skip adding.
+	 */
+	pages = si->pages;
+	if (val == pages) {
+		/* Just like the cmpxchg in del_from_avail_list */
+		if (atomic_long_try_cmpxchg(&si->inuse_pages, &pages,
+					    pages | SWAP_USAGE_OFFLIST_BIT))
+			goto skip;
+	}
+
+	plist_add(&si->avail_list, &swap_avail_head);
+
+skip:
+	spin_unlock(&swap_avail_lock);
+}
+
+/*
+ * swap_usage_add / swap_usage_sub of each slot are serialized by ci->lock
+ * within each cluster, so the total contribution to the global counter should
+ * always be positive and cannot exceed the total number of usable slots.
+ */
+static bool swap_usage_add(struct swap_info_struct *si, unsigned int nr_entries)
+{
+	long val = atomic_long_add_return_relaxed(nr_entries, &si->inuse_pages);
+
+	/*
+	 * If device is full, and SWAP_USAGE_OFFLIST_BIT is not set,
+	 * remove it from the plist.
+	 */
+	if (unlikely(val == si->pages)) {
+		del_from_avail_list(si, false);
+		return true;
+	}
+
+	return false;
+}
+
+static void swap_usage_sub(struct swap_info_struct *si, unsigned int nr_entries)
+{
+	long val = atomic_long_sub_return_relaxed(nr_entries, &si->inuse_pages);
+
+	/*
+	 * If device is not full, and SWAP_USAGE_OFFLIST_BIT is set,
+	 * add it to the plist.
+	 */
+	if (unlikely(val & SWAP_USAGE_OFFLIST_BIT))
+		add_to_avail_list(si, false);
+}
+
+static void swap_range_alloc(struct swap_info_struct *si,
+			     unsigned int nr_entries)
+{
+	if (swap_usage_add(si, nr_entries)) {
+		if (vm_swap_full())
+			schedule_work(&si->reclaim_work);
+	}
+	atomic_long_sub(nr_entries, &nr_swap_pages);
+}
+
+static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
+			    unsigned int nr_entries)
+{
+	unsigned long end = offset + nr_entries - 1;
+	void (*swap_slot_free_notify)(struct block_device *, unsigned long);
+	unsigned int i;
+
+	for (i = 0; i < nr_entries; i++)
+		zswap_invalidate(swp_entry(si->type, offset + i));
+
+	if (si->flags & SWP_BLKDEV)
+		swap_slot_free_notify =
+			si->bdev->bd_disk->fops->swap_slot_free_notify;
+	else
+		swap_slot_free_notify = NULL;
+	while (offset <= end) {
+		arch_swap_invalidate_page(si->type, offset);
+		if (swap_slot_free_notify)
+			swap_slot_free_notify(si->bdev, offset);
+		offset++;
+	}
+
+	/*
+	 * Make sure that try_to_unuse() observes si->inuse_pages reaching 0
+	 * only after the above cleanups are done.
+	 */
+	smp_wmb();
+	atomic_long_add(nr_entries, &nr_swap_pages);
+	swap_usage_sub(si, nr_entries);
+}
+
+static bool get_swap_device_info(struct swap_info_struct *si)
+{
+	if (!percpu_ref_tryget_live(&si->users))
+		return false;
+	/*
+	 * Guarantee the si->users are checked before accessing other
+	 * fields of swap_info_struct, and si->flags (SWP_WRITEOK) is
+	 * up to dated.
+	 *
+	 * Paired with the spin_unlock() after setup_swap_info() in
+	 * enable_swap_info(), and smp_wmb() in swapoff.
+	 */
+	smp_rmb();
+	return true;
+}
+
+/*
+ * Fast path try to get swap entries with specified order from current
+ * CPU's swap entry pool (a cluster).
+ */
+static bool swap_alloc_fast(struct folio *folio)
+{
+	unsigned int order = folio_order(folio);
+	struct swap_cluster_info *ci;
+	struct swap_info_struct *si;
+	unsigned int offset;
+
+	/*
+	 * Once allocated, swap_info_struct will never be completely freed,
+	 * so checking it's liveness by get_swap_device_info is enough.
+	 */
+	si = this_cpu_read(percpu_swap_cluster.si[order]);
+	offset = this_cpu_read(percpu_swap_cluster.offset[order]);
+	if (!si || !offset || !get_swap_device_info(si))
+		return false;
+
+	ci = swap_cluster_lock(si, offset);
+	if (cluster_is_usable(ci, order)) {
+		if (cluster_is_empty(ci))
+			offset = cluster_offset(si, ci);
+		alloc_swap_scan_cluster(si, ci, folio, offset);
+	} else {
+		swap_cluster_unlock(ci);
+	}
+
+	put_swap_device(si);
+	return folio_test_swapcache(folio);
+}
+
+/* Rotate the device and switch to a new cluster */
+static void swap_alloc_slow(struct folio *folio)
+{
+	struct swap_info_struct *si, *next;
+
+	spin_lock(&swap_avail_lock);
+start_over:
+	plist_for_each_entry_safe(si, next, &swap_avail_head, avail_list) {
+		/* Rotate the device and switch to a new cluster */
+		plist_requeue(&si->avail_list, &swap_avail_head);
+		spin_unlock(&swap_avail_lock);
+		if (get_swap_device_info(si)) {
+			cluster_alloc_swap_entry(si, folio);
+			put_swap_device(si);
+			if (folio_test_swapcache(folio))
+				return;
+			if (folio_test_large(folio))
+				return;
+		}
+
+		spin_lock(&swap_avail_lock);
+		/*
+		 * if we got here, it's likely that si was almost full before,
+		 * multiple callers probably all tried to get a page from the
+		 * same si and it filled up before we could get one; or, the si
+		 * filled up between us dropping swap_avail_lock.
+		 * Since we dropped the swap_avail_lock, the swap_avail_list
+		 * may have been modified; so if next is still in the
+		 * swap_avail_head list then try it, otherwise start over if we
+		 * have not gotten any slots.
+		 */
+		if (plist_node_empty(&next->avail_list))
+			goto start_over;
+	}
+	spin_unlock(&swap_avail_lock);
+}
+
+/*
+ * Discard pending clusters in a synchronized way when under high pressure.
+ * Return: true if any cluster is discarded.
+ */
+static bool swap_sync_discard(void)
+{
+	bool ret = false;
+	struct swap_info_struct *si, *next;
+
+	spin_lock(&swap_lock);
+start_over:
+	plist_for_each_entry_safe(si, next, &swap_active_head, list) {
+		spin_unlock(&swap_lock);
+		if (get_swap_device_info(si)) {
+			if (si->flags & SWP_PAGE_DISCARD)
+				ret = swap_do_scheduled_discard(si);
+			put_swap_device(si);
+		}
+		if (ret)
+			return true;
+
+		spin_lock(&swap_lock);
+		if (plist_node_empty(&next->list))
+			goto start_over;
+	}
+	spin_unlock(&swap_lock);
+
+	return false;
+}
+
+static int swap_extend_table_alloc(struct swap_info_struct *si,
+				   struct swap_cluster_info *ci,
+				   unsigned int ci_off, gfp_t gfp)
+{
+	int count;
+	void *table;
+
+	table = kzalloc(sizeof(ci->extend_table[0]) * SWAPFILE_CLUSTER, gfp);
+	if (!table)
+		return -ENOMEM;
+
+	spin_lock(&ci->lock);
+	/*
+	 * Extend table allocation requires releasing ci lock first so it's
+	 * possible that the slot has been freed, no longer overflowed, or
+	 * a concurrent extend table allocation has already succeeded, so
+	 * the allocation is no longer needed.
+	 */
+	if (!cluster_table_is_alloced(ci))
+		goto out_free;
+	count = swp_tb_get_count(__swap_table_get(ci, ci_off));
+	if (count < (SWP_TB_COUNT_MAX - 1))
+		goto out_free;
+	if (ci->extend_table)
+		goto out_free;
+
+	ci->extend_table = table;
+	spin_unlock(&ci->lock);
+	return 0;
+
+out_free:
+	spin_unlock(&ci->lock);
+	kfree(table);
+	return 0;
+}
+
+int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)
+{
+	int ret;
+	struct swap_info_struct *si;
+	struct swap_cluster_info *ci;
+	unsigned long offset = swp_offset(entry);
+
+	si = get_swap_device(entry);
+	if (!si)
+		return 0;
+
+	ci = __swap_offset_to_cluster(si, offset);
+	ret = swap_extend_table_alloc(si, ci, swp_cluster_offset(entry), gfp);
+
+	put_swap_device(si);
+	return ret;
+}
+
+static void swap_extend_table_try_free(struct swap_cluster_info *ci)
+{
+	unsigned long i;
+	bool can_free = true;
+
+	if (!ci->extend_table)
+		return;
+
+	for (i = 0; i < SWAPFILE_CLUSTER; i++) {
+		if (ci->extend_table[i])
+			can_free = false;
+	}
+
+	if (can_free) {
+		kfree(ci->extend_table);
+		ci->extend_table = NULL;
+	}
+}
+
+/* Decrease the swap count of one slot, without freeing it */
+static void __swap_cluster_put_entry(struct swap_cluster_info *ci,
+				    unsigned int ci_off)
+{
+	int count;
+	unsigned long swp_tb;
+
+	lockdep_assert_held(&ci->lock);
+	swp_tb = __swap_table_get(ci, ci_off);
+	count = __swp_tb_get_count(swp_tb);
+
+	VM_WARN_ON_ONCE(count <= 0);
+	VM_WARN_ON_ONCE(count > SWP_TB_COUNT_MAX);
+
+	if (count == SWP_TB_COUNT_MAX) {
+		count = ci->extend_table[ci_off];
+		/* Overflow starts with SWP_TB_COUNT_MAX */
+		VM_WARN_ON_ONCE(count < SWP_TB_COUNT_MAX);
+		count--;
+		if (count == (SWP_TB_COUNT_MAX - 1)) {
+			ci->extend_table[ci_off] = 0;
+			__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, count));
+		} else {
+			ci->extend_table[ci_off] = count;
+		}
+	} else {
+		__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, --count));
+	}
+
+	/*
+	 * `SWP_TB_COUNT_MAX - 1` triggers extend table allocation. If the
+	 * count was above that, then the extend table is no longer needed,
+	 * so free it. And if we just put the count value from MAX - 1, it's
+	 * also possible that a pending dup just attached an extend table.
+	 */
+	if (unlikely(count == SWP_TB_COUNT_MAX - 2 || count == SWP_TB_COUNT_MAX - 1))
+		swap_extend_table_try_free(ci);
+}
+
+/**
+ * swap_put_entries_cluster - Decrease the swap count of slots within one cluster
+ * @si: The swap device.
+ * @offset: start offset of slots.
+ * @nr: number of slots.
+ * @reclaim_cache: if true, also reclaim the swap cache if slots are freed.
+ *
+ * This helper decreases the swap count of a set of slots and tries to
+ * batch free them. Also reclaims the swap cache if @reclaim_cache is true.
+ *
+ * Context: The specified slots must be pinned by existing swap count or swap
+ * cache reference, so they won't be released until this helper returns.
+ */
+static void swap_put_entries_cluster(struct swap_info_struct *si,
+				     pgoff_t offset, int nr,
+				     bool reclaim_cache)
+{
+	struct swap_cluster_info *ci;
+	unsigned int ci_off, ci_end;
+	pgoff_t end = offset + nr;
+	bool need_reclaim = false;
+	unsigned int nr_reclaimed;
+	unsigned long swp_tb;
+	int ci_batch = -1;
+
+	ci = swap_cluster_lock(si, offset);
+	ci_off = offset % SWAPFILE_CLUSTER;
+	ci_end = ci_off + nr;
+	do {
+		swp_tb = __swap_table_get(ci, ci_off);
+		if (swp_tb_get_count(swp_tb) == 1) {
+			/* count == 1 and non-cached slots will be batch freed. */
+			if (!swp_tb_is_folio(swp_tb)) {
+				if (ci_batch == -1)
+					ci_batch = ci_off;
+				continue;
+			}
+			/* count will be 0 after put, slot can be reclaimed */
+			need_reclaim = true;
+		}
+		/*
+		 * A count != 1 or cached slot can't be freed. Put its swap
+		 * count and then free the interrupted pending batch. Cached
+		 * slots will be freed when folio is removed from swap cache
+		 * (__swap_cache_del_folio).
+		 */
+		__swap_cluster_put_entry(ci, ci_off);
+		if (ci_batch != -1) {
+			__swap_cluster_free_entries(si, ci, ci_batch, ci_off - ci_batch);
+			ci_batch = -1;
+		}
+	} while (++ci_off < ci_end);
+
+	if (ci_batch != -1)
+		__swap_cluster_free_entries(si, ci, ci_batch, ci_off - ci_batch);
+	swap_cluster_unlock(ci);
+
+	if (!need_reclaim || !reclaim_cache)
+		return;
+
+	do {
+		nr_reclaimed = __try_to_reclaim_swap(si, offset,
+						     TTRS_UNMAPPED | TTRS_FULL);
+		offset++;
+		if (nr_reclaimed)
+			offset = round_up(offset, abs(nr_reclaimed));
+	} while (offset < end);
+}
+
+/* Increase the swap count of one slot. */
+static int __swap_cluster_dup_entry(struct swap_cluster_info *ci,
+				    unsigned int ci_off)
+{
+	int count;
+	unsigned long swp_tb;
+
+	lockdep_assert_held(&ci->lock);
+	swp_tb = __swap_table_get(ci, ci_off);
+	/* Bad or special slots can't be handled */
+	if (WARN_ON_ONCE(swp_tb_is_bad(swp_tb)))
+		return -EINVAL;
+	count = __swp_tb_get_count(swp_tb);
+	/* Must be either cached or have a count already */
+	if (WARN_ON_ONCE(!count && !swp_tb_is_folio(swp_tb)))
+		return -ENOENT;
+
+	if (likely(count < (SWP_TB_COUNT_MAX - 1))) {
+		__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, count + 1));
+		VM_WARN_ON_ONCE(ci->extend_table && ci->extend_table[ci_off]);
+	} else if (count == (SWP_TB_COUNT_MAX - 1)) {
+		if (ci->extend_table) {
+			VM_WARN_ON_ONCE(ci->extend_table[ci_off]);
+			ci->extend_table[ci_off] = SWP_TB_COUNT_MAX;
+			__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, SWP_TB_COUNT_MAX));
+		} else {
+			return -ENOMEM;
+		}
+	} else if (count == SWP_TB_COUNT_MAX) {
+		VM_WARN_ON_ONCE(ci->extend_table[ci_off] >=
+                               type_max(typeof(ci->extend_table[0])));
+		++ci->extend_table[ci_off];
+	} else {
+		/* Never happens unless counting went wrong */
+		WARN_ON_ONCE(1);
+	}
+
+	return 0;
+}
+
+/**
+ * swap_dup_entries_cluster: Increase the swap count of slots within one cluster.
+ * @si: The swap device.
+ * @offset: start offset of slots.
+ * @nr: number of slots.
+ *
+ * Context: The specified slots must be pinned by existing swap count or swap
+ * cache reference, so they won't be released until this helper returns.
+ * Return: 0 on success. -ENOMEM if the swap count maxed out (SWP_TB_COUNT_MAX)
+ * and failed to allocate an extended table, -EINVAL if any entry is bad entry.
+ */
+static int swap_dup_entries_cluster(struct swap_info_struct *si,
+				    pgoff_t offset, int nr)
+{
+	int err;
+	struct swap_cluster_info *ci;
+	unsigned int ci_start, ci_off, ci_end;
+
+	ci_start = offset % SWAPFILE_CLUSTER;
+	ci_end = ci_start + nr;
+	ci_off = ci_start;
+	ci = swap_cluster_lock(si, offset);
+restart:
+	do {
+		err = __swap_cluster_dup_entry(ci, ci_off);
+		if (unlikely(err)) {
+			if (err == -ENOMEM) {
+				spin_unlock(&ci->lock);
+				err = swap_extend_table_alloc(si, ci, ci_off, GFP_ATOMIC);
+				spin_lock(&ci->lock);
+				if (!err)
+					goto restart;
+			}
+			goto failed;
+		}
+	} while (++ci_off < ci_end);
+	swap_cluster_unlock(ci);
+	return 0;
+failed:
+	while (ci_off-- > ci_start)
+		__swap_cluster_put_entry(ci, ci_off);
+	swap_extend_table_try_free(ci);
+	swap_cluster_unlock(ci);
+	return err;
+}
+
+/**
+ * folio_alloc_swap - allocate swap space for a folio
+ * @folio: folio we want to move to swap
+ *
+ * Allocate swap space for the folio and add the folio to the
+ * swap cache.
+ *
+ * Context: Caller needs to hold the folio lock.
+ * Return: Whether the folio was added to the swap cache.
+ */
+int folio_alloc_swap(struct folio *folio)
+{
+	unsigned int order = folio_order(folio);
+	unsigned int size = 1 << order;
+
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_BUG_ON_FOLIO(!folio_test_uptodate(folio), folio);
+
+	if (order) {
+		/*
+		 * Reject large allocation when THP_SWAP is disabled,
+		 * the caller should split the folio and try again.
+		 */
+		if (!IS_ENABLED(CONFIG_THP_SWAP))
+			return -EAGAIN;
+
+		/*
+		 * Allocation size should never exceed cluster size
+		 * (HPAGE_PMD_SIZE).
+		 */
+		if (size > SWAPFILE_CLUSTER) {
+			VM_WARN_ON_ONCE(1);
+			return -EINVAL;
+		}
+	}
+
+again:
+	local_lock(&percpu_swap_cluster.lock);
+	if (!swap_alloc_fast(folio))
+		swap_alloc_slow(folio);
+	local_unlock(&percpu_swap_cluster.lock);
+
+	if (!order && unlikely(!folio_test_swapcache(folio))) {
+		if (swap_sync_discard())
+			goto again;
+	}
+
+	/* Need to call this even if allocation failed, for MEMCG_SWAP_FAIL. */
+	if (unlikely(mem_cgroup_try_charge_swap(folio)))
+		swap_cache_del_folio(folio);
+
+	if (unlikely(!folio_test_swapcache(folio)))
+		return -ENOMEM;
+
+	return 0;
+}
+
+/**
+ * folio_dup_swap() - Increase swap count of swap entries of a folio.
+ * @folio: folio with swap entries bounded.
+ * @page: if not NULL, only increase the swap count of this page.
+ *
+ * Typically called when the folio is unmapped and have its swap entry to
+ * take its place: Swap entries allocated to a folio has count == 0 and pinned
+ * by swap cache. The swap cache pin doesn't increase the swap count. This
+ * helper sets the initial count == 1 and increases the count as the folio is
+ * unmapped and swap entries referencing the slots are generated to replace
+ * the folio.
+ *
+ * Context: Caller must ensure the folio is locked and in the swap cache.
+ * NOTE: The caller also has to ensure there is no raced call to
+ * swap_put_entries_direct on its swap entry before this helper returns, or
+ * the swap count may underflow.
+ */
+int folio_dup_swap(struct folio *folio, struct page *page)
+{
+	swp_entry_t entry = folio->swap;
+	unsigned long nr_pages = folio_nr_pages(folio);
+
+	VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio);
+
+	if (page) {
+		entry.val += folio_page_idx(folio, page);
+		nr_pages = 1;
+	}
+
+	return swap_dup_entries_cluster(swap_entry_to_info(entry),
+					swp_offset(entry), nr_pages);
+}
+
+/**
+ * folio_put_swap() - Decrease swap count of swap entries of a folio.
+ * @folio: folio with swap entries bounded, must be in swap cache and locked.
+ * @page: if not NULL, only decrease the swap count of this page.
+ *
+ * This won't free the swap slots even if swap count drops to zero, they are
+ * still pinned by the swap cache. User may call folio_free_swap to free them.
+ * Context: Caller must ensure the folio is locked and in the swap cache.
+ */
+void folio_put_swap(struct folio *folio, struct page *page)
+{
+	swp_entry_t entry = folio->swap;
+	unsigned long nr_pages = folio_nr_pages(folio);
+	struct swap_info_struct *si = __swap_entry_to_info(entry);
+
+	VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+	VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio);
+
+	if (page) {
+		entry.val += folio_page_idx(folio, page);
+		nr_pages = 1;
+	}
+
+	swap_put_entries_cluster(si, swp_offset(entry), nr_pages, false);
+}
+
+/*
+ * When we get a swap entry, if there aren't some other ways to
+ * prevent swapoff, such as the folio in swap cache is locked, RCU
+ * reader side is locked, etc., the swap entry may become invalid
+ * because of swapoff.  Then, we need to enclose all swap related
+ * functions with get_swap_device() and put_swap_device(), unless the
+ * swap functions call get/put_swap_device() by themselves.
+ *
+ * RCU reader side lock (including any spinlock) is sufficient to
+ * prevent swapoff, because synchronize_rcu() is called in swapoff()
+ * before freeing data structures.
+ *
+ * Check whether swap entry is valid in the swap device.  If so,
+ * return pointer to swap_info_struct, and keep the swap entry valid
+ * via preventing the swap device from being swapoff, until
+ * put_swap_device() is called.  Otherwise return NULL.
+ *
+ * Notice that swapoff or swapoff+swapon can still happen before the
+ * percpu_ref_tryget_live() in get_swap_device() or after the
+ * percpu_ref_put() in put_swap_device() if there isn't any other way
+ * to prevent swapoff.  The caller must be prepared for that.  For
+ * example, the following situation is possible.
+ *
+ *   CPU1				CPU2
+ *   do_swap_page()
+ *     ...				swapoff+swapon
+ *     swap_cache_alloc_folio()
+ *       // check swap_map
+ *     // verify PTE not changed
+ *
+ * In __swap_duplicate(), the swap_map need to be checked before
+ * changing partly because the specified swap entry may be for another
+ * swap device which has been swapoff.  And in do_swap_page(), after
+ * the page is read from the swap device, the PTE is verified not
+ * changed with the page table locked to check whether the swap device
+ * has been swapoff or swapoff+swapon.
+ */
+struct swap_info_struct *get_swap_device(swp_entry_t entry)
+{
+	struct swap_info_struct *si;
+	unsigned long offset;
+
+	if (!entry.val)
+		goto out;
+	si = swap_entry_to_info(entry);
+	if (!si)
+		goto bad_nofile;
+	if (!get_swap_device_info(si))
+		goto out;
+	offset = swp_offset(entry);
+	if (offset >= si->max)
+		goto put_out;
+
+	return si;
+bad_nofile:
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_file, entry.val);
+out:
+	return NULL;
+put_out:
+	pr_err_ratelimited("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
+	percpu_ref_put(&si->users);
+	return NULL;
+}
+
+/*
+ * Free a set of swap slots after their swap count dropped to zero, or will be
+ * zero after putting the last ref (saves one __swap_cluster_put_entry call).
+ */
+void __swap_cluster_free_entries(struct swap_info_struct *si,
+				 struct swap_cluster_info *ci,
+				 unsigned int ci_start, unsigned int nr_pages)
+{
+	unsigned long old_tb;
+	unsigned short batch_id = 0, id_cur;
+	unsigned int ci_off = ci_start, ci_end = ci_start + nr_pages;
+	unsigned long ci_head = cluster_offset(si, ci);
+	unsigned int batch_off = ci_off;
+
+	VM_WARN_ON(ci->count < nr_pages);
+
+	ci->count -= nr_pages;
+	do {
+		old_tb = __swap_table_get(ci, ci_off);
+		/*
+		 * Freeing is done after release of the last swap count
+		 * ref, or after swap cache is dropped
+		 */
+		VM_WARN_ON(!swp_tb_is_shadow(old_tb) || __swp_tb_get_count(old_tb) > 1);
+
+		/* Resetting the slot to NULL also clears the inline flags. */
+		__swap_table_set(ci, ci_off, null_to_swp_tb());
+		if (!SWAP_TABLE_HAS_ZEROFLAG)
+			__swap_table_clear_zero(ci, ci_off);
+
+		/*
+		 * Uncharge swap slots by memcg in batches. Consecutive
+		 * slots with the same cgroup id are uncharged together.
+		 */
+		id_cur = __swap_cgroup_clear(ci, ci_off, 1);
+		if (batch_id != id_cur) {
+			if (batch_id)
+				mem_cgroup_uncharge_swap(batch_id, ci_off - batch_off);
+			batch_id = id_cur;
+			batch_off = ci_off;
+		}
+	} while (++ci_off < ci_end);
+
+	if (batch_id)
+		mem_cgroup_uncharge_swap(batch_id, ci_off - batch_off);
+
+	swap_range_free(si, ci_head + ci_start, nr_pages);
+	swap_cluster_assert_empty(ci, ci_start, nr_pages, false);
+
+	if (!ci->count)
+		free_cluster(si, ci);
+	else
+		partial_free_cluster(si, ci);
+}
+
+int __swap_count(swp_entry_t entry)
+{
+	struct swap_cluster_info *ci = __swap_entry_to_cluster(entry);
+	unsigned int ci_off = swp_cluster_offset(entry);
+
+	return swp_tb_get_count(__swap_table_get(ci, ci_off));
+}
+
+/**
+ * swap_entry_swapped - Check if the swap entry is swapped.
+ * @si: the swap device.
+ * @entry: the swap entry.
+ */
+bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry)
+{
+	pgoff_t offset = swp_offset(entry);
+	struct swap_cluster_info *ci;
+	unsigned long swp_tb;
+
+	ci = swap_cluster_lock(si, offset);
+	swp_tb = swap_table_get(ci, offset % SWAPFILE_CLUSTER);
+	swap_cluster_unlock(ci);
+
+	return swp_tb_get_count(swp_tb) > 0;
+}
+
+/*
+ * How many references to @entry are currently swapped out?
+ * This returns exact answer.
+ */
+int swp_swapcount(swp_entry_t entry)
+{
+	struct swap_info_struct *si;
+	struct swap_cluster_info *ci;
+	unsigned long swp_tb;
+	int count;
+
+	si = get_swap_device(entry);
+	if (!si)
+		return 0;
+
+	ci = swap_cluster_lock(si, swp_offset(entry));
+	swp_tb = __swap_table_get(ci, swp_cluster_offset(entry));
+	count = swp_tb_get_count(swp_tb);
+	if (count == SWP_TB_COUNT_MAX)
+		count = ci->extend_table[swp_cluster_offset(entry)];
+	swap_cluster_unlock(ci);
+	put_swap_device(si);
+
+	return count < 0 ? 0 : count;
+}
+
+/*
+ * folio_maybe_swapped - Test if a folio covers any swap slot with count > 0.
+ *
+ * Check if a folio is swapped. Holding the folio lock ensures the folio won't
+ * go from not-swapped to swapped because the initial swap count increment can
+ * only be done by folio_dup_swap, which also locks the folio. But a concurrent
+ * decrease of swap count is possible through swap_put_entries_direct, so this
+ * may return a false positive.
+ *
+ * Context: Caller must ensure the folio is locked and in the swap cache.
+ */
+static bool folio_maybe_swapped(struct folio *folio)
+{
+	swp_entry_t entry = folio->swap;
+	struct swap_cluster_info *ci;
+	unsigned int ci_off, ci_end;
+	bool ret = false;
+
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+	VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio);
+
+	ci = __swap_entry_to_cluster(entry);
+	ci_off = swp_cluster_offset(entry);
+	ci_end = ci_off + folio_nr_pages(folio);
+	/*
+	 * Extra locking not needed, folio lock ensures its swap entries
+	 * won't be released, the backing data won't be gone either.
+	 */
+	rcu_read_lock();
+	do {
+		if (__swp_tb_get_count(__swap_table_get(ci, ci_off))) {
+			ret = true;
+			break;
+		}
+	} while (++ci_off < ci_end);
+	rcu_read_unlock();
+
+	return ret;
+}
+
+static bool folio_swapcache_freeable(struct folio *folio)
+{
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	if (!folio_test_swapcache(folio))
+		return false;
+	if (folio_test_writeback(folio))
+		return false;
+
+	/*
+	 * Once hibernation has begun to create its image of memory,
+	 * there's a danger that one of the calls to folio_free_swap()
+	 * - most probably a call from __try_to_reclaim_swap() while
+	 * hibernation is allocating its own swap pages for the image,
+	 * but conceivably even a call from memory reclaim - will free
+	 * the swap from a folio which has already been recorded in the
+	 * image as a clean swapcache folio, and then reuse its swap for
+	 * another page of the image.  On waking from hibernation, the
+	 * original folio might be freed under memory pressure, then
+	 * later read back in from swap, now with the wrong data.
+	 *
+	 * Hibernation suspends storage while it is writing the image
+	 * to disk so check that here.
+	 */
+	if (pm_suspended_storage())
+		return false;
+
+	return true;
+}
+
+/**
+ * folio_free_swap() - Free the swap space used for this folio.
+ * @folio: The folio to remove.
+ *
+ * If swap is getting full, or if there are no more mappings of this folio,
+ * then call folio_free_swap to free its swap space.
+ *
+ * Return: true if we were able to release the swap space.
+ */
+bool folio_free_swap(struct folio *folio)
+{
+	if (!folio_swapcache_freeable(folio))
+		return false;
+	if (folio_maybe_swapped(folio))
+		return false;
+
+	swap_cache_del_folio(folio);
+	folio_set_dirty(folio);
+	return true;
+}
+
+/**
+ * swap_put_entries_direct() - Release reference on range of swap entries and
+ *                             reclaim their cache if no more references remain.
+ * @entry: First entry of range.
+ * @nr: Number of entries in range.
+ *
+ * For each swap entry in the contiguous range, release a reference. If any swap
+ * entries become free, try to reclaim their underlying folios, if present. The
+ * offset range is defined by [entry.offset, entry.offset + nr).
+ *
+ * Context: Caller must ensure there is no race condition on the reference
+ * owner. e.g., locking the PTL of a PTE containing the entry being released.
+ */
+void swap_put_entries_direct(swp_entry_t entry, int nr)
+{
+	const unsigned long start_offset = swp_offset(entry);
+	const unsigned long end_offset = start_offset + nr;
+	unsigned long offset, cluster_end;
+	struct swap_info_struct *si;
+
+	si = get_swap_device(entry);
+	if (WARN_ON_ONCE(!si))
+		return;
+	if (WARN_ON_ONCE(end_offset > si->max))
+		goto out;
+
+	/* Put entries and reclaim cache in each cluster */
+	offset = start_offset;
+	do {
+		cluster_end = min(round_up(offset + 1, SWAPFILE_CLUSTER), end_offset);
+		swap_put_entries_cluster(si, offset, cluster_end - offset, true);
+		offset = cluster_end;
+	} while (offset < end_offset);
+out:
+	put_swap_device(si);
+}
+
+#ifdef CONFIG_HIBERNATION
+/**
+ * swap_alloc_hibernation_slot() - Allocate a swap slot for hibernation.
+ * @type: swap device type index to allocate from.
+ *
+ * The caller must ensure the swap device is stable, either by pinning
+ * it (SWP_HIBERNATION) or by freezing user-space.
+ *
+ * Return: a valid swp_entry_t on success, or an empty entry (val == 0)
+ * on failure.
+ */
+swp_entry_t swap_alloc_hibernation_slot(int type)
+{
+	struct swap_info_struct *pcp_si, *si = swap_type_to_info(type);
+	unsigned long pcp_offset, offset = SWAP_ENTRY_INVALID;
+	struct swap_cluster_info *ci;
+	swp_entry_t entry = {0};
+
+	if (!si)
+		goto fail;
+
+	/*
+	 * Try the local cluster first if it matches the device. If
+	 * not, try grab a new cluster and override local cluster.
+	 */
+	local_lock(&percpu_swap_cluster.lock);
+	pcp_si = this_cpu_read(percpu_swap_cluster.si[0]);
+	pcp_offset = this_cpu_read(percpu_swap_cluster.offset[0]);
+	if (pcp_si == si && pcp_offset) {
+		ci = swap_cluster_lock(si, pcp_offset);
+		if (cluster_is_usable(ci, 0))
+			offset = alloc_swap_scan_cluster(si, ci, NULL, pcp_offset);
+		else
+			swap_cluster_unlock(ci);
+	}
+	if (!offset)
+		offset = cluster_alloc_swap_entry(si, NULL);
+	local_unlock(&percpu_swap_cluster.lock);
+	if (offset)
+		entry = swp_entry(si->type, offset);
+
+fail:
+	return entry;
+}
+
+/**
+ * swap_free_hibernation_slot() - Free a swap slot allocated for hibernation.
+ * @entry: swap entry to free.
+ *
+ * The caller must ensure the swap device is stable.
+ */
+void swap_free_hibernation_slot(swp_entry_t entry)
+{
+	struct swap_info_struct *si = __swap_entry_to_info(entry);
+	struct swap_cluster_info *ci;
+	pgoff_t offset = swp_offset(entry);
+
+	ci = swap_cluster_lock(si, offset);
+	__swap_cluster_put_entry(ci, offset % SWAPFILE_CLUSTER);
+	/*
+	 * A slot with a folio in the swap cache is freed when the folio
+	 * leaves the cache, the same rule swap_put_entries_cluster() follows.
+	 * Readahead can put a folio here, and freeing the slot now would
+	 * leave that folio with no entry behind it.
+	 */
+	if (!swp_tb_is_folio(__swap_table_get(ci, offset % SWAPFILE_CLUSTER)))
+		__swap_cluster_free_entries(si, ci, offset % SWAPFILE_CLUSTER, 1);
+	swap_cluster_unlock(ci);
+
+	/* In theory readahead might add it to the swap cache by accident */
+	__try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
+}
+
+static int __find_hibernation_swap_type(dev_t device, sector_t offset)
+{
+	int type;
+
+	lockdep_assert_held(&swap_lock);
+
+	if (!device)
+		return -EINVAL;
+
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		if (!(sis->flags & SWP_WRITEOK))
+			continue;
+
+		if (device == sis->bdev->bd_dev) {
+			struct swap_extent *se = first_se(sis);
+
+			if (se->start_block == offset)
+				return type;
+		}
+	}
+	return -ENODEV;
+}
+
+/**
+ * pin_hibernation_swap_type - Pin the swap device for hibernation
+ * @device: Block device containing the resume image
+ * @offset: Offset identifying the swap area
+ *
+ * Locate the swap device for @device/@offset and mark it as pinned
+ * for hibernation. While pinned, swapoff() is prevented.
+ *
+ * Only one uswsusp context may pin a swap device at a time.
+ * If already pinned, this function returns -EBUSY.
+ *
+ * Return:
+ * >= 0 on success (swap type).
+ * -EINVAL if @device is invalid.
+ * -ENODEV if the swap device is not found.
+ * -EBUSY if the device is already pinned for hibernation.
+ */
+int pin_hibernation_swap_type(dev_t device, sector_t offset)
+{
+	int type;
+	struct swap_info_struct *si;
+
+	spin_lock(&swap_lock);
+
+	type = __find_hibernation_swap_type(device, offset);
+	if (type < 0) {
+		spin_unlock(&swap_lock);
+		return type;
+	}
+
+	si = swap_type_to_info(type);
+	if (WARN_ON_ONCE(!si)) {
+		spin_unlock(&swap_lock);
+		return -ENODEV;
+	}
+
+	/*
+	 * hibernate_acquire() prevents concurrent hibernation sessions.
+	 * This check additionally guards against double-pinning within
+	 * the same session.
+	 */
+	if (WARN_ON_ONCE(si->flags & SWP_HIBERNATION)) {
+		spin_unlock(&swap_lock);
+		return -EBUSY;
+	}
+
+	si->flags |= SWP_HIBERNATION;
+
+	spin_unlock(&swap_lock);
+	return type;
+}
+
+/**
+ * unpin_hibernation_swap_type - Unpin the swap device for hibernation
+ * @type: Swap type previously returned by pin_hibernation_swap_type()
+ *
+ * Clear the hibernation pin on the given swap device, allowing
+ * swapoff() to proceed normally.
+ *
+ * If @type does not refer to a valid swap device, this function
+ * does nothing.
+ */
+void unpin_hibernation_swap_type(int type)
+{
+	struct swap_info_struct *si;
+
+	spin_lock(&swap_lock);
+	si = swap_type_to_info(type);
+	if (!si) {
+		spin_unlock(&swap_lock);
+		return;
+	}
+	si->flags &= ~SWP_HIBERNATION;
+	spin_unlock(&swap_lock);
+}
+
+/**
+ * find_hibernation_swap_type - Find swap type for hibernation
+ * @device: Block device containing the resume image
+ * @offset: Offset within the device identifying the swap area
+ *
+ * Locate the swap device corresponding to @device and @offset.
+ *
+ * Unlike pin_hibernation_swap_type(), this function only performs a
+ * lookup and does not mark the swap device as pinned for hibernation.
+ *
+ * This is safe in the sysfs-based hibernation path where user space
+ * is already frozen and swapoff() cannot run concurrently.
+ *
+ * Return:
+ * A non-negative swap type on success.
+ * -EINVAL if @device is invalid.
+ * -ENODEV if no matching swap device is found.
+ */
+int find_hibernation_swap_type(dev_t device, sector_t offset)
+{
+	int type;
+
+	spin_lock(&swap_lock);
+	type = __find_hibernation_swap_type(device, offset);
+	spin_unlock(&swap_lock);
+
+	return type;
+}
+
+int find_first_swap(dev_t *device)
+{
+	int type;
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		if (!(sis->flags & SWP_WRITEOK))
+			continue;
+		*device = sis->bdev->bd_dev;
+		spin_unlock(&swap_lock);
+		return type;
+	}
+	spin_unlock(&swap_lock);
+	return -ENODEV;
+}
+
+/*
+ * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
+ * corresponding to given index in swap_info (swap type).
+ */
+sector_t swapdev_block(int type, pgoff_t offset)
+{
+	struct swap_info_struct *si = swap_type_to_info(type);
+	struct swap_extent *se;
+
+	if (!si || !(si->flags & SWP_WRITEOK))
+		return 0;
+	se = offset_to_swap_extent(si, offset);
+	return se->start_block + (offset - se->start_page);
+}
+
+/*
+ * Return either the total number of swap pages of given type, or the number
+ * of free pages of that type (depending on @free)
+ *
+ * This is needed for software suspend
+ */
+unsigned int count_swap_pages(int type, int free)
+{
+	unsigned int n = 0;
+
+	spin_lock(&swap_lock);
+	if ((unsigned int)type < nr_swapfiles) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		spin_lock(&sis->lock);
+		if (sis->flags & SWP_WRITEOK) {
+			n = sis->pages;
+			if (free)
+				n -= swap_usage_in_pages(sis);
+		}
+		spin_unlock(&sis->lock);
+	}
+	spin_unlock(&swap_lock);
+	return n;
+}
+#endif /* CONFIG_HIBERNATION */
+
+static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
+{
+	return pte_same(pte_swp_clear_flags(pte), swp_pte);
+}
+
+/*
+ * No need to decide whether this PTE shares the swap entry with others,
+ * just let do_wp_page work it out if a write is requested later - to
+ * force COW, vm_page_prot omits write permission from any private vma.
+ */
+static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
+		unsigned long addr, swp_entry_t entry, struct folio *folio)
+{
+	struct page *page;
+	struct folio *swapcache;
+	spinlock_t *ptl;
+	pte_t *pte, new_pte, old_pte;
+	bool hwpoisoned = false;
+	int ret = 1;
+
+	/*
+	 * If the folio is removed from swap cache by others, continue to
+	 * unuse other PTEs. try_to_unuse may try again if we missed this one.
+	 */
+	if (!folio_matches_swap_entry(folio, entry))
+		return 0;
+
+	swapcache = folio;
+	folio = ksm_might_need_to_copy(folio, vma, addr);
+	if (unlikely(!folio))
+		return -ENOMEM;
+	else if (unlikely(folio == ERR_PTR(-EHWPOISON))) {
+		hwpoisoned = true;
+		folio = swapcache;
+	}
+
+	page = folio_file_page(folio, swp_offset(entry));
+	if (PageHWPoison(page))
+		hwpoisoned = true;
+
+	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
+	if (unlikely(!pte || !pte_same_as_swp(ptep_get(pte),
+						swp_entry_to_pte(entry)))) {
+		ret = 0;
+		goto out;
+	}
+
+	old_pte = ptep_get(pte);
+
+	if (unlikely(hwpoisoned || !folio_test_uptodate(folio))) {
+		swp_entry_t swp_entry;
+
+		dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
+		if (hwpoisoned) {
+			swp_entry = make_hwpoison_entry(page);
+		} else {
+			swp_entry = make_poisoned_swp_entry();
+		}
+		new_pte = swp_entry_to_pte(swp_entry);
+		ret = 0;
+		goto setpte;
+	}
+
+	/*
+	 * Some architectures may have to restore extra metadata to the page
+	 * when reading from swap. This metadata may be indexed by swap entry
+	 * so this must be called before folio_put_swap().
+	 */
+	arch_swap_restore(folio_swap(entry, folio), folio);
+
+	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
+	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
+	folio_get(folio);
+	if (folio == swapcache) {
+		rmap_t rmap_flags = RMAP_NONE;
+
+		/*
+		 * See do_swap_page(): writeback would be problematic.
+		 * However, we do a folio_wait_writeback() just before this
+		 * call and have the folio locked.
+		 */
+		VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
+		if (pte_swp_exclusive(old_pte))
+			rmap_flags |= RMAP_EXCLUSIVE;
+		/*
+		 * We currently only expect small !anon folios, which are either
+		 * fully exclusive or fully shared. If we ever get large folios
+		 * here, we have to be careful.
+		 */
+		if (!folio_test_anon(folio)) {
+			VM_WARN_ON_ONCE(folio_test_large(folio));
+			VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
+			folio_add_new_anon_rmap(folio, vma, addr, rmap_flags);
+		} else {
+			folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flags);
+		}
+	} else { /* ksm created a completely new copy */
+		folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE);
+		folio_add_lru_vma(folio, vma);
+	}
+	new_pte = pte_mkold(mk_pte(page, vma->vm_page_prot));
+	if (pte_swp_soft_dirty(old_pte))
+		new_pte = pte_mksoft_dirty(new_pte);
+	if (pte_swp_uffd(old_pte))
+		new_pte = pte_mkuffd(new_pte);
+
+	/* See do_swap_page(): restore PAGE_NONE for RWP */
+	if (pte_swp_uffd(old_pte) && userfaultfd_rwp(vma))
+		new_pte = pte_modify(new_pte, PAGE_NONE);
+
+setpte:
+	set_pte_at(vma->vm_mm, addr, pte, new_pte);
+	folio_put_swap(swapcache, folio_file_page(swapcache, swp_offset(entry)));
+out:
+	if (pte)
+		pte_unmap_unlock(pte, ptl);
+	if (folio != swapcache) {
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+	return ret;
+}
+
+static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
+			unsigned long addr, unsigned long end,
+			unsigned int type)
+{
+	pte_t *pte = NULL;
+
+	do {
+		struct folio *folio;
+		unsigned long swp_tb;
+		softleaf_t entry;
+		int ret;
+		pte_t ptent;
+
+		if (!pte++) {
+			pte = pte_offset_map(pmd, addr);
+			if (!pte)
+				break;
+		}
+
+		ptent = ptep_get_lockless(pte);
+		entry = softleaf_from_pte(ptent);
+
+		if (!softleaf_is_swap(entry))
+			continue;
+		if (swp_type(entry) != type)
+			continue;
+
+		pte_unmap(pte);
+		pte = NULL;
+
+		folio = swap_cache_get_folio(entry);
+		if (!folio) {
+			struct vm_fault vmf = {
+				.vma = vma,
+				.address = addr,
+				.real_address = addr,
+				.pmd = pmd,
+			};
+
+			folio = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
+						&vmf);
+		}
+		if (!folio) {
+			swp_tb = swap_table_get(__swap_entry_to_cluster(entry),
+						swp_cluster_offset(entry));
+			if (swp_tb_get_count(swp_tb) <= 0)
+				continue;
+			return -ENOMEM;
+		}
+
+		folio_lock(folio);
+		folio_wait_writeback(folio);
+		ret = unuse_pte(vma, pmd, addr, entry, folio);
+		if (ret < 0) {
+			folio_unlock(folio);
+			folio_put(folio);
+			return ret;
+		}
+
+		folio_free_swap(folio);
+		folio_unlock(folio);
+		folio_put(folio);
+	} while (addr += PAGE_SIZE, addr != end);
+
+	if (pte)
+		pte_unmap(pte);
+	return 0;
+}
+
+static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
+				unsigned long addr, unsigned long end,
+				unsigned int type)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int ret;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		cond_resched();
+		next = pmd_addr_end(addr, end);
+		ret = unuse_pte_range(vma, pmd, addr, next, type);
+		if (ret)
+			return ret;
+	} while (pmd++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d,
+				unsigned long addr, unsigned long end,
+				unsigned int type)
+{
+	pud_t *pud;
+	unsigned long next;
+	int ret;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		ret = unuse_pmd_range(vma, pud, addr, next, type);
+		if (ret)
+			return ret;
+	} while (pud++, addr = next, addr != end);
+	return 0;
+}
+
+static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd,
+				unsigned long addr, unsigned long end,
+				unsigned int type)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int ret;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (p4d_none_or_clear_bad(p4d))
+			continue;
+		ret = unuse_pud_range(vma, p4d, addr, next, type);
+		if (ret)
+			return ret;
+	} while (p4d++, addr = next, addr != end);
+	return 0;
+}
+
+static int unuse_vma(struct vm_area_struct *vma, unsigned int type)
+{
+	pgd_t *pgd;
+	unsigned long addr, end, next;
+	int ret;
+
+	addr = vma->vm_start;
+	end = vma->vm_end;
+
+	pgd = pgd_offset(vma->vm_mm, addr);
+	do {
+		next = pgd_addr_end(addr, end);
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		ret = unuse_p4d_range(vma, pgd, addr, next, type);
+		if (ret)
+			return ret;
+	} while (pgd++, addr = next, addr != end);
+	return 0;
+}
+
+static int unuse_mm(struct mm_struct *mm, unsigned int type)
+{
+	struct vm_area_struct *vma;
+	int ret = 0;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	mmap_read_lock(mm);
+	if (check_stable_address_space(mm))
+		goto unlock;
+	for_each_vma(vmi, vma) {
+		if (vma->anon_vma && !is_vm_hugetlb_page(vma)) {
+			ret = unuse_vma(vma, type);
+			if (ret)
+				break;
+		}
+
+		cond_resched();
+	}
+unlock:
+	mmap_read_unlock(mm);
+	return ret;
+}
+
+/*
+ * Scan swap table from current position to next entry still in use.
+ * Return 0 if there are no inuse entries after prev till end of
+ * the map.
+ */
+static unsigned int find_next_to_unuse(struct swap_info_struct *si,
+					unsigned int prev)
+{
+	unsigned int i;
+	unsigned long swp_tb;
+
+	/*
+	 * No need for swap_lock here: we're just looking
+	 * for whether an entry is in use, not modifying it; false
+	 * hits are okay, and sys_swapoff() has already prevented new
+	 * allocations from this area (while holding swap_lock).
+	 */
+	for (i = prev + 1; i < si->max; i++) {
+		swp_tb = swap_table_get(__swap_offset_to_cluster(si, i),
+					i % SWAPFILE_CLUSTER);
+		if (!swp_tb_is_null(swp_tb) && !swp_tb_is_bad(swp_tb))
+			break;
+		if ((i % LATENCY_LIMIT) == 0)
+			cond_resched();
+	}
+
+	if (i == si->max)
+		i = 0;
+
+	return i;
+}
+
+static int try_to_unuse(unsigned int type)
+{
+	struct mm_struct *prev_mm;
+	struct mm_struct *mm;
+	struct list_head *p;
+	int retval = 0;
+	struct swap_info_struct *si = swap_info[type];
+	struct folio *folio;
+	swp_entry_t entry;
+	unsigned int i;
+
+	if (!swap_usage_in_pages(si))
+		goto success;
+
+retry:
+	retval = shmem_unuse(type);
+	if (retval)
+		return retval;
+
+	prev_mm = &init_mm;
+	mmget(prev_mm);
+
+	spin_lock(&mmlist_lock);
+	p = &init_mm.mmlist;
+	while (swap_usage_in_pages(si) &&
+	       !signal_pending(current) &&
+	       (p = p->next) != &init_mm.mmlist) {
+
+		mm = list_entry(p, struct mm_struct, mmlist);
+		if (!mmget_not_zero(mm))
+			continue;
+		spin_unlock(&mmlist_lock);
+		mmput(prev_mm);
+		prev_mm = mm;
+		retval = unuse_mm(mm, type);
+		if (retval) {
+			mmput(prev_mm);
+			return retval;
+		}
+
+		/*
+		 * Make sure that we aren't completely killing
+		 * interactive performance.
+		 */
+		cond_resched();
+		spin_lock(&mmlist_lock);
+	}
+	spin_unlock(&mmlist_lock);
+
+	mmput(prev_mm);
+
+	i = 0;
+	while (swap_usage_in_pages(si) &&
+	       !signal_pending(current) &&
+	       (i = find_next_to_unuse(si, i)) != 0) {
+
+		entry = swp_entry(type, i);
+		folio = swap_cache_get_folio(entry);
+		if (!folio)
+			continue;
+
+		/*
+		 * It is conceivable that a racing task removed this folio from
+		 * swap cache just before we acquired the page lock. The folio
+		 * might even be back in swap cache on another swap area. But
+		 * that is okay, folio_free_swap() only removes stale folios.
+		 */
+		folio_lock(folio);
+		folio_wait_writeback(folio);
+		folio_free_swap(folio);
+		folio_unlock(folio);
+		folio_put(folio);
+	}
+
+	/*
+	 * Lets check again to see if there are still swap entries in the map.
+	 * If yes, we would need to do retry the unuse logic again.
+	 * Under global memory pressure, swap entries can be reinserted back
+	 * into process space after the mmlist loop above passes over them.
+	 *
+	 * Limit the number of retries? No: when mmget_not_zero()
+	 * above fails, that mm is likely to be freeing swap from
+	 * exit_mmap(), which proceeds at its own independent pace;
+	 * and even shmem_writeout() could have been preempted after
+	 * folio_alloc_swap(), temporarily hiding that swap.  It's easy
+	 * and robust (though cpu-intensive) just to keep retrying.
+	 */
+	if (swap_usage_in_pages(si)) {
+		if (!signal_pending(current))
+			goto retry;
+		return -EINTR;
+	}
+
+success:
+	/*
+	 * Make sure that further cleanups after try_to_unuse() returns happen
+	 * after swap_range_free() reduces si->inuse_pages to 0.
+	 */
+	smp_mb();
+	return 0;
+}
+
+/*
+ * After a successful try_to_unuse, if no swap is now in use, we know
+ * we can empty the mmlist.  swap_lock must be held on entry and exit.
+ * Note that mmlist_lock nests inside swap_lock, and an mm must be
+ * added to the mmlist just after page_duplicate - before would be racy.
+ */
+static void drain_mmlist(void)
+{
+	struct list_head *p, *next;
+	unsigned int type;
+
+	for (type = 0; type < nr_swapfiles; type++)
+		if (swap_usage_in_pages(swap_info[type]))
+			return;
+	spin_lock(&mmlist_lock);
+	list_for_each_safe(p, next, &init_mm.mmlist)
+		list_del_init(p);
+	spin_unlock(&mmlist_lock);
+}
+
+/*
+ * Free all of a swapdev's extent information
+ */
+static void destroy_swap_extents(struct swap_info_struct *sis,
+				 struct file *swap_file)
+{
+	while (!RB_EMPTY_ROOT(&sis->swap_extent_root)) {
+		struct rb_node *rb = sis->swap_extent_root.rb_node;
+		struct swap_extent *se = rb_entry(rb, struct swap_extent, rb_node);
+
+		rb_erase(rb, &sis->swap_extent_root);
+		kfree(se);
+	}
+
+	if (sis->flags & SWP_ACTIVATED) {
+		struct address_space *mapping = swap_file->f_mapping;
+
+		sis->flags &= ~SWP_ACTIVATED;
+		if (mapping->a_ops->swap_deactivate)
+			mapping->a_ops->swap_deactivate(swap_file);
+	}
+}
+
+/*
+ * Add a block range (and the corresponding page range) into this swapdev's
+ * extent tree.
+ *
+ * This function rather assumes that it is called in ascending page order.
+ */
+int
+add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
+		unsigned long nr_pages, sector_t start_block)
+{
+	struct rb_node **link = &sis->swap_extent_root.rb_node, *parent = NULL;
+	struct swap_extent *se;
+	struct swap_extent *new_se;
+
+	/*
+	 * place the new node at the right most since the
+	 * function is called in ascending page order.
+	 */
+	while (*link) {
+		parent = *link;
+		link = &parent->rb_right;
+	}
+
+	if (parent) {
+		se = rb_entry(parent, struct swap_extent, rb_node);
+		BUG_ON(se->start_page + se->nr_pages != start_page);
+		if (se->start_block + se->nr_pages == start_block) {
+			/* Merge it */
+			se->nr_pages += nr_pages;
+			return 0;
+		}
+	}
+
+	/* No merge, insert a new extent. */
+	new_se = kmalloc_obj(*se);
+	if (new_se == NULL)
+		return -ENOMEM;
+	new_se->start_page = start_page;
+	new_se->nr_pages = nr_pages;
+	new_se->start_block = start_block;
+
+	rb_link_node(&new_se->rb_node, parent, link);
+	rb_insert_color(&new_se->rb_node, &sis->swap_extent_root);
+	return 1;
+}
+EXPORT_SYMBOL_GPL(add_swap_extent);
+
+/*
+ * A `swap extent' is a simple thing which maps a contiguous range of pages
+ * onto a contiguous range of disk blocks.  A rbtree of swap extents is
+ * built at swapon time and is then used at swap_writepage/swap_read_folio
+ * time for locating where on disk a page belongs.
+ *
+ * If the swapfile is an S_ISBLK block device, a single extent is installed.
+ * This is done so that the main operating code can treat S_ISBLK and S_ISREG
+ * swap files identically.
+ *
+ * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
+ * extent rbtree operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
+ * swapfiles are handled *identically* after swapon time.
+ *
+ * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
+ * and will parse them into a rbtree, in PAGE_SIZE chunks.  If some stray
+ * blocks are found which do not fall within the PAGE_SIZE alignment
+ * requirements, they are simply tossed out - we will never use those blocks
+ * for swapping.
+ *
+ * For all swap devices we set S_SWAPFILE across the life of the swapon.  This
+ * prevents users from writing to the swap device, which will corrupt memory.
+ *
+ * The amount of disk space which a single swap extent represents varies.
+ * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
+ * extents in the rbtree. - akpm.
+ */
+static int setup_swap_extents(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;
+	int ret;
+
+	ret = sio_pool_init();
+	if (ret)
+		return ret;
+
+	sis->ops = &swap_bdev_ops;
+
+	if (S_ISBLK(inode->i_mode)) {
+		ret = add_swap_extent(sis, 0, sis->max, 0);
+		*span = sis->pages;
+		return ret;
+	}
+
+	if (mapping->a_ops->swap_activate) {
+		ret = mapping->a_ops->swap_activate(sis, swap_file, span);
+		if (ret < 0)
+			return ret;
+		sis->flags |= SWP_ACTIVATED;
+		return ret;
+	}
+
+	return generic_swapfile_activate(sis, swap_file, span);
+}
+
+static void _enable_swap_info(struct swap_info_struct *si)
+{
+	atomic_long_add(si->pages, &nr_swap_pages);
+	total_swap_pages += si->pages;
+
+	assert_spin_locked(&swap_lock);
+
+	plist_add(&si->list, &swap_active_head);
+
+	/* Add back to available list */
+	add_to_avail_list(si, true);
+}
+
+/*
+ * Called after the swap device is ready, resurrect its percpu ref, it's now
+ * safe to reference it. Add it to the list to expose it to the allocator.
+ */
+static void enable_swap_info(struct swap_info_struct *si)
+{
+	percpu_ref_resurrect(&si->users);
+	spin_lock(&swap_lock);
+	spin_lock(&si->lock);
+	_enable_swap_info(si);
+	spin_unlock(&si->lock);
+	spin_unlock(&swap_lock);
+}
+
+static void reinsert_swap_info(struct swap_info_struct *si)
+{
+	spin_lock(&swap_lock);
+	spin_lock(&si->lock);
+	_enable_swap_info(si);
+	spin_unlock(&si->lock);
+	spin_unlock(&swap_lock);
+}
+
+/*
+ * Called after clearing SWP_WRITEOK, ensures cluster_alloc_range
+ * see the updated flags, so there will be no more allocations.
+ */
+static void wait_for_allocation(struct swap_info_struct *si)
+{
+	unsigned long offset;
+	unsigned long end = ALIGN(si->max, SWAPFILE_CLUSTER);
+	struct swap_cluster_info *ci;
+
+	BUG_ON(si->flags & SWP_WRITEOK);
+
+	for (offset = 0; offset < end; offset += SWAPFILE_CLUSTER) {
+		ci = swap_cluster_lock(si, offset);
+		swap_cluster_unlock(ci);
+	}
+}
+
+static void free_swap_cluster_info(struct swap_cluster_info *cluster_info,
+				   unsigned long maxpages)
+{
+	struct swap_cluster_info *ci;
+	int i, nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
+
+	if (!cluster_info)
+		return;
+	for (i = 0; i < nr_clusters; i++) {
+		ci = cluster_info + i;
+		/* Cluster with bad marks count will have a remaining table */
+		spin_lock(&ci->lock);
+		if (cluster_table_is_alloced(ci)) {
+			swap_cluster_assert_empty(ci, 0, SWAPFILE_CLUSTER, true);
+			swap_cluster_free_table(ci);
+		}
+		spin_unlock(&ci->lock);
+	}
+	kvfree(cluster_info);
+}
+
+/*
+ * Called after swap device's reference count is dead, so
+ * neither scan nor allocation will use it.
+ */
+static void flush_percpu_swap_cluster(struct swap_info_struct *si)
+{
+	int cpu, i;
+	struct swap_info_struct **pcp_si;
+
+	for_each_possible_cpu(cpu) {
+		pcp_si = per_cpu_ptr(percpu_swap_cluster.si, cpu);
+		/*
+		 * Invalidate the percpu swap cluster cache, si->users
+		 * is dead, so no new user will point to it, just flush
+		 * any existing user.
+		 */
+		for (i = 0; i < SWAP_NR_ORDERS; i++)
+			cmpxchg(&pcp_si[i], si, NULL);
+	}
+}
+
+
+SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
+{
+	struct swap_info_struct *p = NULL;
+	struct swap_cluster_info *cluster_info;
+	struct file *swap_file, *victim;
+	struct address_space *mapping;
+	struct inode *inode;
+	unsigned int maxpages;
+	int err, found = 0;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	BUG_ON(!current->mm);
+
+	CLASS(filename, pathname)(specialfile);
+	victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
+	if (IS_ERR(victim))
+		return PTR_ERR(victim);
+
+	mapping = victim->f_mapping;
+	spin_lock(&swap_lock);
+	plist_for_each_entry(p, &swap_active_head, list) {
+		if (p->flags & SWP_WRITEOK) {
+			if (p->swap_file->f_mapping == mapping) {
+				found = 1;
+				break;
+			}
+		}
+	}
+	if (!found) {
+		err = -EINVAL;
+		spin_unlock(&swap_lock);
+		goto out_dput;
+	}
+
+	/* Refuse swapoff while the device is pinned for hibernation */
+	if (p->flags & SWP_HIBERNATION) {
+		err = -EBUSY;
+		spin_unlock(&swap_lock);
+		goto out_dput;
+	}
+
+	if (!security_vm_enough_memory_mm(current->mm, p->pages))
+		vm_unacct_memory(p->pages);
+	else {
+		err = -ENOMEM;
+		spin_unlock(&swap_lock);
+		goto out_dput;
+	}
+	spin_lock(&p->lock);
+	del_from_avail_list(p, true);
+	plist_del(&p->list, &swap_active_head);
+	atomic_long_sub(p->pages, &nr_swap_pages);
+	total_swap_pages -= p->pages;
+	spin_unlock(&p->lock);
+	spin_unlock(&swap_lock);
+
+	wait_for_allocation(p);
+
+	set_current_oom_origin();
+	err = try_to_unuse(p->type);
+	clear_current_oom_origin();
+
+	if (err) {
+		/* re-insert swap space back into swap_list */
+		reinsert_swap_info(p);
+		goto out_dput;
+	}
+
+	/*
+	 * Wait for swap operations protected by get/put_swap_device()
+	 * to complete.  Because of synchronize_rcu() here, all swap
+	 * operations protected by RCU reader side lock (including any
+	 * spinlock) will be waited too.  This makes it easy to
+	 * prevent folio_test_swapcache() and the following swap cache
+	 * operations from racing with swapoff.
+	 */
+	percpu_ref_kill(&p->users);
+	synchronize_rcu();
+	wait_for_completion(&p->comp);
+
+	flush_work(&p->discard_work);
+	flush_work(&p->reclaim_work);
+	flush_percpu_swap_cluster(p);
+
+	destroy_swap_extents(p, p->swap_file);
+
+	if (!(p->flags & SWP_SOLIDSTATE))
+		atomic_dec(&nr_rotate_swap);
+
+	mutex_lock(&swapon_mutex);
+	spin_lock(&swap_lock);
+	spin_lock(&p->lock);
+	drain_mmlist();
+
+	swap_file = p->swap_file;
+	p->swap_file = NULL;
+	maxpages = p->max;
+	cluster_info = p->cluster_info;
+	p->max = 0;
+	p->cluster_info = NULL;
+	spin_unlock(&p->lock);
+	spin_unlock(&swap_lock);
+	arch_swap_invalidate_area(p->type);
+	zswap_swapoff(p->type);
+	mutex_unlock(&swapon_mutex);
+	kfree(p->global_cluster);
+	p->global_cluster = NULL;
+	free_swap_cluster_info(cluster_info, maxpages);
+
+	inode = mapping->host;
+
+	inode_lock(inode);
+	inode->i_flags &= ~S_SWAPFILE;
+	inode_unlock(inode);
+	filp_close(swap_file, NULL);
+
+	/*
+	 * Clear the SWP_USED flag after all resources are freed so that swapon
+	 * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
+	 * not hold p->lock after we cleared its SWP_WRITEOK.
+	 */
+	spin_lock(&swap_lock);
+	p->flags = 0;
+	spin_unlock(&swap_lock);
+
+	err = 0;
+	atomic_inc(&proc_poll_event);
+	wake_up_interruptible(&proc_poll_wait);
+
+out_dput:
+	filp_close(victim, NULL);
+	return err;
+}
+
+#ifdef CONFIG_PROC_FS
+static __poll_t swaps_poll(struct file *file, poll_table *wait)
+{
+	struct seq_file *seq = file->private_data;
+
+	poll_wait(file, &proc_poll_wait, wait);
+
+	if (seq->poll_event != atomic_read(&proc_poll_event)) {
+		seq->poll_event = atomic_read(&proc_poll_event);
+		return EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLPRI;
+	}
+
+	return EPOLLIN | EPOLLRDNORM;
+}
+
+/* iterator */
+static void *swap_start(struct seq_file *swap, loff_t *pos)
+{
+	struct swap_info_struct *si;
+	int type;
+	loff_t l = *pos;
+
+	mutex_lock(&swapon_mutex);
+
+	if (!l)
+		return SEQ_START_TOKEN;
+
+	for (type = 0; (si = swap_type_to_info(type)); type++) {
+		if (!(si->swap_file))
+			continue;
+		if (!--l)
+			return si;
+	}
+
+	return NULL;
+}
+
+static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
+{
+	struct swap_info_struct *si = v;
+	int type;
+
+	if (v == SEQ_START_TOKEN)
+		type = 0;
+	else
+		type = si->type + 1;
+
+	++(*pos);
+	for (; (si = swap_type_to_info(type)); type++) {
+		if (!(si->swap_file))
+			continue;
+		return si;
+	}
+
+	return NULL;
+}
+
+static void swap_stop(struct seq_file *swap, void *v)
+{
+	mutex_unlock(&swapon_mutex);
+}
+
+static int swap_show(struct seq_file *swap, void *v)
+{
+	struct swap_info_struct *si = v;
+	struct file *file;
+	int len;
+	unsigned long bytes, inuse;
+
+	if (si == SEQ_START_TOKEN) {
+		seq_puts(swap, "Filename\t\t\t\tType\t\tSize\t\tUsed\t\tPriority\n");
+		return 0;
+	}
+
+	bytes = K(si->pages);
+	inuse = K(swap_usage_in_pages(si));
+
+	file = si->swap_file;
+	len = seq_file_path(swap, file, " \t\n\\");
+	seq_printf(swap, "%*s%s\t%lu\t%s%lu\t%s%d\n",
+			len < 40 ? 40 - len : 1, " ",
+			S_ISBLK(file_inode(file)->i_mode) ?
+				"partition" : "file\t",
+			bytes, bytes < 10000000 ? "\t" : "",
+			inuse, inuse < 10000000 ? "\t" : "",
+			si->prio);
+	return 0;
+}
+
+static const struct seq_operations swaps_op = {
+	.start =	swap_start,
+	.next =		swap_next,
+	.stop =		swap_stop,
+	.show =		swap_show
+};
+
+static int swaps_open(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq;
+	int ret;
+
+	ret = seq_open(file, &swaps_op);
+	if (ret)
+		return ret;
+
+	seq = file->private_data;
+	seq->poll_event = atomic_read(&proc_poll_event);
+	return 0;
+}
+
+static const struct proc_ops swaps_proc_ops = {
+	.proc_flags	= PROC_ENTRY_PERMANENT,
+	.proc_open	= swaps_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= seq_release,
+	.proc_poll	= swaps_poll,
+};
+
+static int __init procswaps_init(void)
+{
+	proc_create("swaps", 0, NULL, &swaps_proc_ops);
+	return 0;
+}
+__initcall(procswaps_init);
+#endif /* CONFIG_PROC_FS */
+
+#ifdef MAX_SWAPFILES_CHECK
+static int __init max_swapfiles_check(void)
+{
+	MAX_SWAPFILES_CHECK();
+	return 0;
+}
+late_initcall(max_swapfiles_check);
+#endif
+
+static struct swap_info_struct *alloc_swap_info(void)
+{
+	struct swap_info_struct *p;
+	struct swap_info_struct *defer = NULL;
+	unsigned int type;
+
+	p = kvzalloc_obj(struct swap_info_struct);
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	if (percpu_ref_init(&p->users, swap_users_ref_free,
+			    PERCPU_REF_INIT_DEAD, GFP_KERNEL)) {
+		kvfree(p);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		if (!(swap_info[type]->flags & SWP_USED))
+			break;
+	}
+	if (type >= MAX_SWAPFILES) {
+		spin_unlock(&swap_lock);
+		percpu_ref_exit(&p->users);
+		kvfree(p);
+		return ERR_PTR(-EPERM);
+	}
+	if (type >= nr_swapfiles) {
+		p->type = type;
+		/*
+		 * Publish the swap_info_struct after initializing it.
+		 * Note that kvzalloc() above zeroes all its fields.
+		 */
+		smp_store_release(&swap_info[type], p); /* rcu_assign_pointer() */
+		nr_swapfiles++;
+	} else {
+		defer = p;
+		p = swap_info[type];
+		/*
+		 * Do not memset this entry: a racing procfs swap_next()
+		 * would be relying on p->type to remain valid.
+		 */
+	}
+	p->swap_extent_root = RB_ROOT;
+	plist_node_init(&p->list, 0);
+	plist_node_init(&p->avail_list, 0);
+	p->flags = SWP_USED;
+	spin_unlock(&swap_lock);
+	if (defer) {
+		percpu_ref_exit(&defer->users);
+		kvfree(defer);
+	}
+	spin_lock_init(&p->lock);
+	atomic_long_set(&p->inuse_pages, SWAP_USAGE_OFFLIST_BIT);
+	init_completion(&p->comp);
+
+	return p;
+}
+
+static int claim_swapfile(struct swap_info_struct *si, struct inode *inode)
+{
+	if (S_ISBLK(inode->i_mode)) {
+		si->bdev = I_BDEV(inode);
+		/*
+		 * Zoned block devices contain zones that have a sequential
+		 * write only restriction.  Hence zoned block devices are not
+		 * suitable for swapping.  Disallow them here.
+		 */
+		if (bdev_is_zoned(si->bdev))
+			return -EINVAL;
+		si->flags |= SWP_BLKDEV;
+	} else if (S_ISREG(inode->i_mode)) {
+		si->bdev = inode->i_sb->s_bdev;
+	}
+
+	return 0;
+}
+
+
+/*
+ * Find out how many pages are allowed for a single swap device. There
+ * are two limiting factors:
+ * 1) the number of bits for the swap offset in the swp_entry_t type, and
+ * 2) the number of bits in the swap pte, as defined by the different
+ * architectures.
+ *
+ * In order to find the largest possible bit mask, a swap entry with
+ * swap type 0 and swap offset ~0UL is created, encoded to a swap pte,
+ * decoded to a swp_entry_t again, and finally the swap offset is
+ * extracted.
+ *
+ * This will mask all the bits from the initial ~0UL mask that can't
+ * be encoded in either the swp_entry_t or the architecture definition
+ * of a swap pte.
+ */
+unsigned long generic_max_swapfile_size(void)
+{
+	swp_entry_t entry = swp_entry(0, ~0UL);
+	const pte_t pte = softleaf_to_pte(entry);
+
+	/*
+	 * Since the PTE can be an invalid softleaf entry (e.g. the none PTE),
+	 * we need to do this manually.
+	 */
+	entry = __pte_to_swp_entry(pte);
+	entry = swp_entry(__swp_type(entry), __swp_offset(entry));
+
+	return swp_offset(entry) + 1;
+}
+
+/* Can be overridden by an architecture for additional checks. */
+__weak unsigned long arch_max_swapfile_size(void)
+{
+	return generic_max_swapfile_size();
+}
+
+static unsigned long read_swap_header(struct swap_info_struct *si,
+					union swap_header *swap_header,
+					struct inode *inode)
+{
+	int i;
+	unsigned long maxpages;
+	unsigned long swapfilepages;
+	unsigned long last_page;
+
+	if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
+		pr_err("Unable to find swap-space signature\n");
+		return 0;
+	}
+
+	/* swap partition endianness hack... */
+	if (swab32(swap_header->info.version) == 1) {
+		swab32s(&swap_header->info.version);
+		swab32s(&swap_header->info.last_page);
+		swab32s(&swap_header->info.nr_badpages);
+		if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+			return 0;
+		for (i = 0; i < swap_header->info.nr_badpages; i++)
+			swab32s(&swap_header->info.badpages[i]);
+	}
+	/* Check the swap header's sub-version */
+	if (swap_header->info.version != 1) {
+		pr_warn("Unable to handle swap header version %d\n",
+			swap_header->info.version);
+		return 0;
+	}
+
+	maxpages = swapfile_maximum_size;
+	last_page = swap_header->info.last_page;
+	if (!last_page) {
+		pr_warn("Empty swap-file\n");
+		return 0;
+	}
+	if (last_page > maxpages) {
+		pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
+			K(maxpages), K(last_page));
+	}
+	if (maxpages > last_page) {
+		maxpages = last_page + 1;
+		/* p->max is an unsigned int: don't overflow it */
+		if ((unsigned int)maxpages == 0)
+			maxpages = UINT_MAX;
+	}
+
+	if (!maxpages)
+		return 0;
+	swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
+	if (swapfilepages && maxpages > swapfilepages) {
+		pr_warn("Swap area shorter than signature indicates\n");
+		return 0;
+	}
+	if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
+		return 0;
+	if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+		return 0;
+
+	return maxpages;
+}
+
+static int setup_swap_clusters_info(struct swap_info_struct *si,
+				    union swap_header *swap_header,
+				    unsigned long maxpages)
+{
+	unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
+	struct swap_cluster_info *cluster_info;
+	int err = -ENOMEM;
+	unsigned long i;
+
+	cluster_info = kvzalloc_objs(*cluster_info, nr_clusters);
+	if (!cluster_info)
+		goto err;
+
+	for (i = 0; i < nr_clusters; i++)
+		spin_lock_init(&cluster_info[i].lock);
+
+	if (!(si->flags & SWP_SOLIDSTATE)) {
+		si->global_cluster = kmalloc_obj(*si->global_cluster);
+		if (!si->global_cluster)
+			goto err;
+		for (i = 0; i < SWAP_NR_ORDERS; i++)
+			si->global_cluster->next[i] = SWAP_ENTRY_INVALID;
+		spin_lock_init(&si->global_cluster_lock);
+	}
+
+	/*
+	 * Mark unusable pages (header page, bad pages, and the EOF part of
+	 * the last cluster) as unavailable. The clusters aren't marked free
+	 * yet, so no list operations are involved yet.
+	 */
+	err = swap_cluster_setup_bad_slot(si, cluster_info, 0, false);
+	if (err)
+		goto err;
+	for (i = 0; i < swap_header->info.nr_badpages; i++) {
+		unsigned int page_nr = swap_header->info.badpages[i];
+
+		if (!page_nr || page_nr > swap_header->info.last_page) {
+			pr_warn("Bad slot offset is out of border: %d (last_page: %d)\n",
+				page_nr, swap_header->info.last_page);
+			err = -EINVAL;
+			goto err;
+		}
+		err = swap_cluster_setup_bad_slot(si, cluster_info, page_nr, false);
+		if (err)
+			goto err;
+	}
+	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++) {
+		err = swap_cluster_setup_bad_slot(si, cluster_info, i, true);
+		if (err)
+			goto err;
+	}
+
+	INIT_LIST_HEAD(&si->free_clusters);
+	INIT_LIST_HEAD(&si->full_clusters);
+	INIT_LIST_HEAD(&si->discard_clusters);
+
+	for (i = 0; i < SWAP_NR_ORDERS; i++) {
+		INIT_LIST_HEAD(&si->nonfull_clusters[i]);
+		INIT_LIST_HEAD(&si->frag_clusters[i]);
+	}
+
+	for (i = 0; i < nr_clusters; i++) {
+		struct swap_cluster_info *ci = &cluster_info[i];
+
+		if (ci->count) {
+			ci->flags = CLUSTER_FLAG_NONFULL;
+			list_add_tail(&ci->list, &si->nonfull_clusters[0]);
+		} else {
+			ci->flags = CLUSTER_FLAG_FREE;
+			list_add_tail(&ci->list, &si->free_clusters);
+		}
+	}
+
+	si->cluster_info = cluster_info;
+	return 0;
+err:
+	free_swap_cluster_info(cluster_info, maxpages);
+	return err;
+}
+
+SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
+{
+	struct swap_info_struct *si;
+	struct file *swap_file = NULL;
+	struct address_space *mapping;
+	struct dentry *dentry;
+	int prio;
+	int error;
+	union swap_header *swap_header;
+	int nr_extents;
+	sector_t span;
+	unsigned long maxpages;
+	struct folio *folio = NULL;
+	struct inode *inode = NULL;
+	bool inced_nr_rotate_swap = false;
+
+	if (swap_flags & ~SWAP_FLAGS_VALID)
+		return -EINVAL;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	/*
+	 * Allocate or reuse existing !SWP_USED swap_info. The returned
+	 * si will stay in a dying status, so nothing will access its content
+	 * until enable_swap_info resurrects its percpu ref and expose it.
+	 */
+	si = alloc_swap_info();
+	if (IS_ERR(si))
+		return PTR_ERR(si);
+
+	INIT_WORK(&si->discard_work, swap_discard_work);
+	INIT_WORK(&si->reclaim_work, swap_reclaim_work);
+
+	CLASS(filename, name)(specialfile);
+	swap_file = file_open_name(name, O_RDWR | O_LARGEFILE | O_EXCL, 0);
+	if (IS_ERR(swap_file)) {
+		error = PTR_ERR(swap_file);
+		swap_file = NULL;
+		goto bad_swap;
+	}
+
+	mapping = swap_file->f_mapping;
+	dentry = swap_file->f_path.dentry;
+	inode = mapping->host;
+
+	error = claim_swapfile(si, inode);
+	if (unlikely(error))
+		goto bad_swap;
+
+	inode_lock(inode);
+	if (d_unlinked(dentry) || cant_mount(dentry)) {
+		error = -ENOENT;
+		goto bad_swap_unlock_inode;
+	}
+	if (IS_SWAPFILE(inode)) {
+		error = -EBUSY;
+		goto bad_swap_unlock_inode;
+	}
+	if (IS_ENCRYPTED(inode)) {
+		pr_warn_once(
+			"Filesystem-level encrypted swapfile '%s' is unsupported. Create a loop device over it, or use dm-crypt\n",
+			name->name);
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
+
+	/*
+	 * The swap subsystem needs a major overhaul to support this.
+	 * It doesn't work yet so just disable it for now.
+	 */
+	if (mapping_min_folio_order(mapping) > 0) {
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
+
+	/*
+	 * Read the swap header.
+	 */
+	if (!mapping->a_ops->read_folio) {
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
+	folio = read_mapping_folio(mapping, 0, swap_file);
+	if (IS_ERR(folio)) {
+		error = PTR_ERR(folio);
+		goto bad_swap_unlock_inode;
+	}
+	swap_header = kmap_local_folio(folio, 0);
+
+	maxpages = read_swap_header(si, swap_header, inode);
+	if (unlikely(!maxpages)) {
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
+
+	si->max = maxpages;
+	si->pages = maxpages - 1;
+	nr_extents = setup_swap_extents(si, swap_file, &span);
+	if (nr_extents < 0) {
+		error = nr_extents;
+		goto bad_swap_unlock_inode;
+	}
+	if (si->pages != si->max - 1) {
+		pr_err("swap:%u != (max:%u - 1)\n", si->pages, si->max);
+		error = -EINVAL;
+		goto bad_swap_unlock_inode;
+	}
+
+	maxpages = si->max;
+
+	/* Set up the swap cluster info */
+	error = setup_swap_clusters_info(si, swap_header, maxpages);
+	if (error)
+		goto bad_swap_unlock_inode;
+
+	if (si->bdev && bdev_stable_writes(si->bdev))
+		si->flags |= SWP_STABLE_WRITES;
+
+	if (si->bdev && bdev_synchronous(si->bdev))
+		si->flags |= SWP_SYNCHRONOUS_IO;
+
+	if (si->bdev && !bdev_rot(si->bdev)) {
+		si->flags |= SWP_SOLIDSTATE;
+	} else {
+		atomic_inc(&nr_rotate_swap);
+		inced_nr_rotate_swap = true;
+	}
+
+	if ((swap_flags & SWAP_FLAG_DISCARD) &&
+	    si->bdev && bdev_max_discard_sectors(si->bdev)) {
+		/*
+		 * When discard is enabled for swap with no particular
+		 * policy flagged, we set all swap discard flags here in
+		 * order to sustain backward compatibility with older
+		 * swapon(8) releases.
+		 */
+		si->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
+			     SWP_PAGE_DISCARD);
+
+		/*
+		 * By flagging sys_swapon, a sysadmin can tell us to
+		 * either do single-time area discards only, or to just
+		 * perform discards for released swap page-clusters.
+		 * Now it's time to adjust the p->flags accordingly.
+		 */
+		if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
+			si->flags &= ~SWP_PAGE_DISCARD;
+		else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
+			si->flags &= ~SWP_AREA_DISCARD;
+
+		/* issue a swapon-time discard if it's still required */
+		if (si->flags & SWP_AREA_DISCARD) {
+			int err = discard_swap(si);
+			if (unlikely(err))
+				pr_err("swapon: discard_swap(%p): %d\n",
+					si, err);
+		}
+	}
+
+	error = zswap_swapon(si->type, maxpages);
+	if (error)
+		goto bad_swap_unlock_inode;
+
+	/*
+	 * Flush any pending IO and dirty mappings before we start using this
+	 * swap device.
+	 */
+	inode->i_flags |= S_SWAPFILE;
+	error = inode_drain_writes(inode);
+	if (error) {
+		inode->i_flags &= ~S_SWAPFILE;
+		goto free_swap_zswap;
+	}
+
+	mutex_lock(&swapon_mutex);
+	prio = DEF_SWAP_PRIO;
+	if (swap_flags & SWAP_FLAG_PREFER)
+		prio = swap_flags & SWAP_FLAG_PRIO_MASK;
+
+	/*
+	 * The plist prio is negated because plist ordering is
+	 * low-to-high, while swap ordering is high-to-low
+	 */
+	si->prio = prio;
+	si->list.prio = -si->prio;
+	si->avail_list.prio = -si->prio;
+	si->swap_file = swap_file;
+
+	/* Sets SWP_WRITEOK, resurrect the percpu ref, expose the swap device */
+	enable_swap_info(si);
+
+	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
+		K(si->pages), name->name, si->prio, nr_extents,
+		K((unsigned long long)span),
+		(si->flags & SWP_SOLIDSTATE) ? "SS" : "",
+		(si->flags & SWP_DISCARDABLE) ? "D" : "",
+		(si->flags & SWP_AREA_DISCARD) ? "s" : "",
+		(si->flags & SWP_PAGE_DISCARD) ? "c" : "");
+
+	mutex_unlock(&swapon_mutex);
+	atomic_inc(&proc_poll_event);
+	wake_up_interruptible(&proc_poll_wait);
+
+	error = 0;
+	goto out;
+free_swap_zswap:
+	zswap_swapoff(si->type);
+bad_swap_unlock_inode:
+	inode_unlock(inode);
+bad_swap:
+	kfree(si->global_cluster);
+	si->global_cluster = NULL;
+	inode = NULL;
+	destroy_swap_extents(si, swap_file);
+	free_swap_cluster_info(si->cluster_info, si->max);
+	si->cluster_info = NULL;
+	/*
+	 * Clear the SWP_USED flag after all resources are freed so
+	 * alloc_swap_info can reuse this si safely.
+	 */
+	spin_lock(&swap_lock);
+	si->flags = 0;
+	spin_unlock(&swap_lock);
+	if (inced_nr_rotate_swap)
+		atomic_dec(&nr_rotate_swap);
+	if (swap_file)
+		filp_close(swap_file, NULL);
+out:
+	if (!IS_ERR_OR_NULL(folio))
+		folio_release_kmap(folio, swap_header);
+	if (inode)
+		inode_unlock(inode);
+	return error;
+}
+
+void si_swapinfo(struct sysinfo *val)
+{
+	unsigned int type;
+	unsigned long nr_to_be_unused = 0;
+
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *si = swap_info[type];
+
+		if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
+			nr_to_be_unused += swap_usage_in_pages(si);
+	}
+	val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
+	val->totalswap = total_swap_pages + nr_to_be_unused;
+	spin_unlock(&swap_lock);
+}
+
+/*
+ * swap_dup_entry_direct() - Increase reference count of a swap entry by one.
+ * @entry: first swap entry from which we want to increase the refcount.
+ *
+ * Returns 0 for success, or -ENOMEM if the extend table is required
+ * but could not be atomically allocated.  Returns -EINVAL if the swap
+ * entry is invalid, which might occur if a page table entry has got
+ * corrupted.
+ *
+ * Context: Caller must ensure there is no race condition on the reference
+ * owner. e.g., locking the PTL of a PTE containing the entry being increased.
+ * Also the swap entry must have a count >= 1. Otherwise folio_dup_swap should
+ * be used.
+ */
+int swap_dup_entry_direct(swp_entry_t entry)
+{
+	struct swap_info_struct *si;
+
+	si = swap_entry_to_info(entry);
+	if (WARN_ON_ONCE(!si)) {
+		pr_err_ratelimited("%s%08lx\n", Bad_file, entry.val);
+		return -EINVAL;
+	}
+
+	/*
+	 * The caller must be increasing the swap count from a direct
+	 * reference of the swap slot (e.g. a swap entry in page table).
+	 * So the swap count must be >= 1.
+	 */
+	VM_WARN_ON_ONCE(!swap_entry_swapped(si, entry));
+
+	return swap_dup_entries_cluster(si, swp_offset(entry), 1);
+}
+
+#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
+static bool __has_usable_swap(void)
+{
+	return !plist_head_empty(&swap_active_head);
+}
+
+void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
+{
+	struct swap_info_struct *si;
+
+	if (!(gfp & __GFP_IO))
+		return;
+
+	if (!__has_usable_swap())
+		return;
+
+	if (!blk_cgroup_congested())
+		return;
+
+	/*
+	 * We've already scheduled a throttle, avoid taking the global swap
+	 * lock.
+	 */
+	if (current->throttle_disk)
+		return;
+
+	spin_lock(&swap_avail_lock);
+	plist_for_each_entry(si, &swap_avail_head, avail_list) {
+		if (si->bdev) {
+			blkcg_schedule_throttle(si->bdev->bd_disk, true);
+			break;
+		}
+	}
+	spin_unlock(&swap_avail_lock);
+}
+#endif
+
+static int __init swapfile_init(void)
+{
+	swapfile_maximum_size = arch_max_swapfile_size();
+
+	/*
+	 * Once a cluster is freed, it's swap table content is read
+	 * only, and all swap cache readers (swap_cache_*) verifies
+	 * the content before use. So it's safe to use RCU slab here.
+	 */
+	if (!SWP_TABLE_USE_PAGE)
+		swap_table_cachep = kmem_cache_create("swap_table",
+				    sizeof(struct swap_table),
+				    0, SLAB_PANIC | SLAB_TYPESAFE_BY_RCU, NULL);
+
+#ifdef CONFIG_MIGRATION
+	if (swapfile_maximum_size >= (1UL << SWP_MIG_TOTAL_BITS))
+		swap_migration_ad_supported = true;
+#endif	/* CONFIG_MIGRATION */
+
+	return 0;
+}
+subsys_initcall(swapfile_init);