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linux/mm/swapfile.c
Huang Ying d4a34d7fb4 mm,swap: add document about RCU read lock and swapoff interaction 
During reviewing a patch to fix the race condition between
free_swap_and_cache() and swapoff() [1], it was found that the document
about how to prevent racing with swapoff isn't clear enough.  Especially
RCU read lock can prevent swapoff from freeing data structures.  So, the
document is added as comments.

[1] https://lore.kernel.org/linux-mm/c8fe62d0-78b8-527a-5bef-ee663ccdc37a@huawei.com/

Link: https://lkml.kernel.org/r/20240407065450.498821-1-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-05-05 17:53:26 -07:00

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// 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/swap_slots.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/swapops.h>
#include <linux/swap_cgroup.h>
#include "internal.h"
#include "swap.h"
static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
unsigned char);
static void free_swap_count_continuations(struct swap_info_struct *);
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;
static int least_priority = -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 Unused_file[] = "Unused swap file entry ";
static const char Bad_offset[] = "Bad swap offset entry ";
static const char Unused_offset[] = "Unused 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 struct plist_head *swap_avail_heads;
static DEFINE_SPINLOCK(swap_avail_lock);
static struct swap_info_struct *swap_info[MAX_SWAPFILES];
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);
static struct swap_info_struct *swap_type_to_swap_info(int type)
{
if (type >= MAX_SWAPFILES)
return NULL;
return READ_ONCE(swap_info[type]); /* rcu_dereference() */
}
static inline unsigned char swap_count(unsigned char ent)
{
return ent & ~SWAP_HAS_CACHE; /* may include COUNT_CONTINUED flag */
}
/* 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
/*
* 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)
{
swp_entry_t entry = swp_entry(si->type, offset);
struct folio *folio;
int ret = 0;
folio = filemap_get_folio(swap_address_space(entry), offset);
if (IS_ERR(folio))
return 0;
/*
* When this function is called from scan_swap_map_slots() and it's
* called by vmscan.c at reclaiming folios. So 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)) {
if ((flags & TTRS_ANYWAY) ||
((flags & TTRS_UNMAPPED) && !folio_mapped(folio)) ||
((flags & TTRS_FULL) && mem_cgroup_swap_full(folio)))
ret = folio_free_swap(folio);
folio_unlock(folio);
}
ret = ret ? folio_nr_pages(folio) : -folio_nr_pages(folio);
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 = swp_swap_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);
}
}
#ifdef CONFIG_THP_SWAP
#define SWAPFILE_CLUSTER HPAGE_PMD_NR
#define swap_entry_order(order) (order)
#else
#define SWAPFILE_CLUSTER 256
/*
* Define swap_entry_order() as constant to let compiler to optimize
* out some code if !CONFIG_THP_SWAP
*/
#define swap_entry_order(order) 0
#endif
#define LATENCY_LIMIT 256
static inline void cluster_set_flag(struct swap_cluster_info *info,
unsigned int flag)
{
info->flags = flag;
}
static inline unsigned int cluster_count(struct swap_cluster_info *info)
{
return info->data;
}
static inline void cluster_set_count(struct swap_cluster_info *info,
unsigned int c)
{
info->data = c;
}
static inline void cluster_set_count_flag(struct swap_cluster_info *info,
unsigned int c, unsigned int f)
{
info->flags = f;
info->data = c;
}
static inline unsigned int cluster_next(struct swap_cluster_info *info)
{
return info->data;
}
static inline void cluster_set_next(struct swap_cluster_info *info,
unsigned int n)
{
info->data = n;
}
static inline void cluster_set_next_flag(struct swap_cluster_info *info,
unsigned int n, unsigned int f)
{
info->flags = f;
info->data = n;
}
static inline bool cluster_is_free(struct swap_cluster_info *info)
{
return info->flags & CLUSTER_FLAG_FREE;
}
static inline bool cluster_is_null(struct swap_cluster_info *info)
{
return info->flags & CLUSTER_FLAG_NEXT_NULL;
}
static inline void cluster_set_null(struct swap_cluster_info *info)
{
info->flags = CLUSTER_FLAG_NEXT_NULL;
info->data = 0;
}
static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
unsigned long offset)
{
struct swap_cluster_info *ci;
ci = si->cluster_info;
if (ci) {
ci += offset / SWAPFILE_CLUSTER;
spin_lock(&ci->lock);
}
return ci;
}
static inline void unlock_cluster(struct swap_cluster_info *ci)
{
if (ci)
spin_unlock(&ci->lock);
}
/*
* Determine the locking method in use for this device. Return
* swap_cluster_info if SSD-style cluster-based locking is in place.
*/
static inline struct swap_cluster_info *lock_cluster_or_swap_info(
struct swap_info_struct *si, unsigned long offset)
{
struct swap_cluster_info *ci;
/* Try to use fine-grained SSD-style locking if available: */
ci = lock_cluster(si, offset);
/* Otherwise, fall back to traditional, coarse locking: */
if (!ci)
spin_lock(&si->lock);
return ci;
}
static inline void unlock_cluster_or_swap_info(struct swap_info_struct *si,
struct swap_cluster_info *ci)
{
if (ci)
unlock_cluster(ci);
else
spin_unlock(&si->lock);
}
static inline bool cluster_list_empty(struct swap_cluster_list *list)
{
return cluster_is_null(&list->head);
}
static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
{
return cluster_next(&list->head);
}
static void cluster_list_init(struct swap_cluster_list *list)
{
cluster_set_null(&list->head);
cluster_set_null(&list->tail);
}
static void cluster_list_add_tail(struct swap_cluster_list *list,
struct swap_cluster_info *ci,
unsigned int idx)
{
if (cluster_list_empty(list)) {
cluster_set_next_flag(&list->head, idx, 0);
cluster_set_next_flag(&list->tail, idx, 0);
} else {
struct swap_cluster_info *ci_tail;
unsigned int tail = cluster_next(&list->tail);
/*
* Nested cluster lock, but both cluster locks are
* only acquired when we held swap_info_struct->lock
*/
ci_tail = ci + tail;
spin_lock_nested(&ci_tail->lock, SINGLE_DEPTH_NESTING);
cluster_set_next(ci_tail, idx);
spin_unlock(&ci_tail->lock);
cluster_set_next_flag(&list->tail, idx, 0);
}
}
static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
struct swap_cluster_info *ci)
{
unsigned int idx;
idx = cluster_next(&list->head);
if (cluster_next(&list->tail) == idx) {
cluster_set_null(&list->head);
cluster_set_null(&list->tail);
} else
cluster_set_next_flag(&list->head,
cluster_next(&ci[idx]), 0);
return idx;
}
/* Add a cluster to discard list and schedule it to do discard */
static void swap_cluster_schedule_discard(struct swap_info_struct *si,
unsigned int idx)
{
/*
* If scan_swap_map_slots() can't find a free cluster, it will check
* si->swap_map directly. To make sure the discarding cluster isn't
* taken by scan_swap_map_slots(), mark the swap entries bad (occupied).
* It will be cleared after discard
*/
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
SWAP_MAP_BAD, SWAPFILE_CLUSTER);
cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
schedule_work(&si->discard_work);
}
static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
{
struct swap_cluster_info *ci = si->cluster_info;
cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE);
cluster_list_add_tail(&si->free_clusters, ci, idx);
}
/*
* Doing discard actually. After a cluster discard is finished, the cluster
* will be added to free cluster list. caller should hold si->lock.
*/
static void swap_do_scheduled_discard(struct swap_info_struct *si)
{
struct swap_cluster_info *info, *ci;
unsigned int idx;
info = si->cluster_info;
while (!cluster_list_empty(&si->discard_clusters)) {
idx = cluster_list_del_first(&si->discard_clusters, info);
spin_unlock(&si->lock);
discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
SWAPFILE_CLUSTER);
spin_lock(&si->lock);
ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
__free_cluster(si, idx);
memset(si->swap_map + idx * SWAPFILE_CLUSTER,
0, SWAPFILE_CLUSTER);
unlock_cluster(ci);
}
}
static void swap_discard_work(struct work_struct *work)
{
struct swap_info_struct *si;
si = container_of(work, struct swap_info_struct, discard_work);
spin_lock(&si->lock);
swap_do_scheduled_discard(si);
spin_unlock(&si->lock);
}
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);
}
static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
{
struct swap_cluster_info *ci = si->cluster_info;
VM_BUG_ON(cluster_list_first(&si->free_clusters) != idx);
cluster_list_del_first(&si->free_clusters, ci);
cluster_set_count_flag(ci + idx, 0, 0);
}
static void free_cluster(struct swap_info_struct *si, unsigned long idx)
{
struct swap_cluster_info *ci = si->cluster_info + idx;
VM_BUG_ON(cluster_count(ci) != 0);
/*
* 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, idx);
return;
}
__free_cluster(si, idx);
}
/*
* The cluster corresponding to page_nr will be used. The cluster will be
* removed from free cluster list and its usage counter will be increased by
* count.
*/
static void add_cluster_info_page(struct swap_info_struct *p,
struct swap_cluster_info *cluster_info, unsigned long page_nr,
unsigned long count)
{
unsigned long idx = page_nr / SWAPFILE_CLUSTER;
if (!cluster_info)
return;
if (cluster_is_free(&cluster_info[idx]))
alloc_cluster(p, idx);
VM_BUG_ON(cluster_count(&cluster_info[idx]) + count > SWAPFILE_CLUSTER);
cluster_set_count(&cluster_info[idx],
cluster_count(&cluster_info[idx]) + count);
}
/*
* The cluster corresponding to page_nr will be used. The cluster will be
* removed from free cluster list and its usage counter will be increased by 1.
*/
static void inc_cluster_info_page(struct swap_info_struct *p,
struct swap_cluster_info *cluster_info, unsigned long page_nr)
{
add_cluster_info_page(p, cluster_info, page_nr, 1);
}
/*
* The cluster corresponding to page_nr decreases one usage. If the usage
* counter becomes 0, which means no page in the cluster is in using, we can
* optionally discard the cluster and add it to free cluster list.
*/
static void dec_cluster_info_page(struct swap_info_struct *p,
struct swap_cluster_info *cluster_info, unsigned long page_nr)
{
unsigned long idx = page_nr / SWAPFILE_CLUSTER;
if (!cluster_info)
return;
VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
cluster_set_count(&cluster_info[idx],
cluster_count(&cluster_info[idx]) - 1);
if (cluster_count(&cluster_info[idx]) == 0)
free_cluster(p, idx);
}
/*
* It's possible scan_swap_map_slots() uses a free cluster in the middle of free
* cluster list. Avoiding such abuse to avoid list corruption.
*/
static bool
scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
unsigned long offset, int order)
{
struct percpu_cluster *percpu_cluster;
bool conflict;
offset /= SWAPFILE_CLUSTER;
conflict = !cluster_list_empty(&si->free_clusters) &&
offset != cluster_list_first(&si->free_clusters) &&
cluster_is_free(&si->cluster_info[offset]);
if (!conflict)
return false;
percpu_cluster = this_cpu_ptr(si->percpu_cluster);
percpu_cluster->next[order] = SWAP_NEXT_INVALID;
return true;
}
static inline bool swap_range_empty(char *swap_map, unsigned int start,
unsigned int nr_pages)
{
unsigned int i;
for (i = 0; i < nr_pages; i++) {
if (swap_map[start + i])
return false;
}
return true;
}
/*
* Try to get swap entries with specified order from current cpu's swap entry
* pool (a cluster). This might involve allocating a new cluster for current CPU
* too.
*/
static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
unsigned long *offset, unsigned long *scan_base, int order)
{
unsigned int nr_pages = 1 << order;
struct percpu_cluster *cluster;
struct swap_cluster_info *ci;
unsigned int tmp, max;
new_cluster:
cluster = this_cpu_ptr(si->percpu_cluster);
tmp = cluster->next[order];
if (tmp == SWAP_NEXT_INVALID) {
if (!cluster_list_empty(&si->free_clusters)) {
tmp = cluster_next(&si->free_clusters.head) *
SWAPFILE_CLUSTER;
} else if (!cluster_list_empty(&si->discard_clusters)) {
/*
* we don't have free cluster but have some clusters in
* discarding, do discard now and reclaim them, then
* reread cluster_next_cpu since we dropped si->lock
*/
swap_do_scheduled_discard(si);
*scan_base = this_cpu_read(*si->cluster_next_cpu);
*offset = *scan_base;
goto new_cluster;
} else
return false;
}
/*
* Other CPUs can use our cluster if they can't find a free cluster,
* check if there is still free entry in the cluster, maintaining
* natural alignment.
*/
max = min_t(unsigned long, si->max, ALIGN(tmp + 1, SWAPFILE_CLUSTER));
if (tmp < max) {
ci = lock_cluster(si, tmp);
while (tmp < max) {
if (swap_range_empty(si->swap_map, tmp, nr_pages))
break;
tmp += nr_pages;
}
unlock_cluster(ci);
}
if (tmp >= max) {
cluster->next[order] = SWAP_NEXT_INVALID;
goto new_cluster;
}
*offset = tmp;
*scan_base = tmp;
tmp += nr_pages;
cluster->next[order] = tmp < max ? tmp : SWAP_NEXT_INVALID;
return true;
}
static void __del_from_avail_list(struct swap_info_struct *p)
{
int nid;
assert_spin_locked(&p->lock);
for_each_node(nid)
plist_del(&p->avail_lists[nid], &swap_avail_heads[nid]);
}
static void del_from_avail_list(struct swap_info_struct *p)
{
spin_lock(&swap_avail_lock);
__del_from_avail_list(p);
spin_unlock(&swap_avail_lock);
}
static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
unsigned int nr_entries)
{
unsigned int end = offset + nr_entries - 1;
if (offset == si->lowest_bit)
si->lowest_bit += nr_entries;
if (end == si->highest_bit)
WRITE_ONCE(si->highest_bit, si->highest_bit - nr_entries);
WRITE_ONCE(si->inuse_pages, si->inuse_pages + nr_entries);
if (si->inuse_pages == si->pages) {
si->lowest_bit = si->max;
si->highest_bit = 0;
del_from_avail_list(si);
}
}
static void add_to_avail_list(struct swap_info_struct *p)
{
int nid;
spin_lock(&swap_avail_lock);
for_each_node(nid)
plist_add(&p->avail_lists[nid], &swap_avail_heads[nid]);
spin_unlock(&swap_avail_lock);
}
static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
unsigned int nr_entries)
{
unsigned long begin = offset;
unsigned long end = offset + nr_entries - 1;
void (*swap_slot_free_notify)(struct block_device *, unsigned long);
if (offset < si->lowest_bit)
si->lowest_bit = offset;
if (end > si->highest_bit) {
bool was_full = !si->highest_bit;
WRITE_ONCE(si->highest_bit, end);
if (was_full && (si->flags & SWP_WRITEOK))
add_to_avail_list(si);
}
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++;
}
clear_shadow_from_swap_cache(si->type, begin, end);
/*
* 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);
WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries);
}
static void set_cluster_next(struct swap_info_struct *si, unsigned long next)
{
unsigned long prev;
if (!(si->flags & SWP_SOLIDSTATE)) {
si->cluster_next = next;
return;
}
prev = this_cpu_read(*si->cluster_next_cpu);
/*
* Cross the swap address space size aligned trunk, choose
* another trunk randomly to avoid lock contention on swap
* address space if possible.
*/
if ((prev >> SWAP_ADDRESS_SPACE_SHIFT) !=
(next >> SWAP_ADDRESS_SPACE_SHIFT)) {
/* No free swap slots available */
if (si->highest_bit <= si->lowest_bit)
return;
next = get_random_u32_inclusive(si->lowest_bit, si->highest_bit);
next = ALIGN_DOWN(next, SWAP_ADDRESS_SPACE_PAGES);
next = max_t(unsigned int, next, si->lowest_bit);
}
this_cpu_write(*si->cluster_next_cpu, next);
}
static bool swap_offset_available_and_locked(struct swap_info_struct *si,
unsigned long offset)
{
if (data_race(!si->swap_map[offset])) {
spin_lock(&si->lock);
return true;
}
if (vm_swap_full() && READ_ONCE(si->swap_map[offset]) == SWAP_HAS_CACHE) {
spin_lock(&si->lock);
return true;
}
return false;
}
static int scan_swap_map_slots(struct swap_info_struct *si,
unsigned char usage, int nr,
swp_entry_t slots[], int order)
{
struct swap_cluster_info *ci;
unsigned long offset;
unsigned long scan_base;
unsigned long last_in_cluster = 0;
int latency_ration = LATENCY_LIMIT;
unsigned int nr_pages = 1 << order;
int n_ret = 0;
bool scanned_many = false;
/*
* We try to cluster swap pages by allocating them sequentially
* in swap. Once we've allocated SWAPFILE_CLUSTER pages this
* way, however, we resort to first-free allocation, starting
* a new cluster. This prevents us from scattering swap pages
* all over the entire swap partition, so that we reduce
* overall disk seek times between swap pages. -- sct
* But we do now try to find an empty cluster. -Andrea
* And we let swap pages go all over an SSD partition. Hugh
*/
if (order > 0) {
/*
* Should not even be attempting large allocations when huge
* page swap is disabled. Warn and fail the allocation.
*/
if (!IS_ENABLED(CONFIG_THP_SWAP) ||
nr_pages > SWAPFILE_CLUSTER) {
VM_WARN_ON_ONCE(1);
return 0;
}
/*
* Swapfile is not block device or not using clusters so unable
* to allocate large entries.
*/
if (!(si->flags & SWP_BLKDEV) || !si->cluster_info)
return 0;
}
si->flags += SWP_SCANNING;
/*
* Use percpu scan base for SSD to reduce lock contention on
* cluster and swap cache. For HDD, sequential access is more
* important.
*/
if (si->flags & SWP_SOLIDSTATE)
scan_base = this_cpu_read(*si->cluster_next_cpu);
else
scan_base = si->cluster_next;
offset = scan_base;
/* SSD algorithm */
if (si->cluster_info) {
if (!scan_swap_map_try_ssd_cluster(si, &offset, &scan_base, order)) {
if (order > 0)
goto no_page;
goto scan;
}
} else if (unlikely(!si->cluster_nr--)) {
if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
si->cluster_nr = SWAPFILE_CLUSTER - 1;
goto checks;
}
spin_unlock(&si->lock);
/*
* If seek is expensive, start searching for new cluster from
* start of partition, to minimize the span of allocated swap.
* If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
* case, just handled by scan_swap_map_try_ssd_cluster() above.
*/
scan_base = offset = si->lowest_bit;
last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
/* Locate the first empty (unaligned) cluster */
for (; last_in_cluster <= si->highest_bit; offset++) {
if (si->swap_map[offset])
last_in_cluster = offset + SWAPFILE_CLUSTER;
else if (offset == last_in_cluster) {
spin_lock(&si->lock);
offset -= SWAPFILE_CLUSTER - 1;
si->cluster_next = offset;
si->cluster_nr = SWAPFILE_CLUSTER - 1;
goto checks;
}
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
}
}
offset = scan_base;
spin_lock(&si->lock);
si->cluster_nr = SWAPFILE_CLUSTER - 1;
}
checks:
if (si->cluster_info) {
while (scan_swap_map_ssd_cluster_conflict(si, offset, order)) {
/* take a break if we already got some slots */
if (n_ret)
goto done;
if (!scan_swap_map_try_ssd_cluster(si, &offset,
&scan_base, order)) {
if (order > 0)
goto no_page;
goto scan;
}
}
}
if (!(si->flags & SWP_WRITEOK))
goto no_page;
if (!si->highest_bit)
goto no_page;
if (offset > si->highest_bit)
scan_base = offset = si->lowest_bit;
ci = lock_cluster(si, offset);
/* reuse swap entry of cache-only swap if not busy. */
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
int swap_was_freed;
unlock_cluster(ci);
spin_unlock(&si->lock);
swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
spin_lock(&si->lock);
/* entry was freed successfully, try to use this again */
if (swap_was_freed > 0)
goto checks;
goto scan; /* check next one */
}
if (si->swap_map[offset]) {
unlock_cluster(ci);
if (!n_ret)
goto scan;
else
goto done;
}
memset(si->swap_map + offset, usage, nr_pages);
add_cluster_info_page(si, si->cluster_info, offset, nr_pages);
unlock_cluster(ci);
swap_range_alloc(si, offset, nr_pages);
slots[n_ret++] = swp_entry(si->type, offset);
/* got enough slots or reach max slots? */
if ((n_ret == nr) || (offset >= si->highest_bit))
goto done;
/* search for next available slot */
/* time to take a break? */
if (unlikely(--latency_ration < 0)) {
if (n_ret)
goto done;
spin_unlock(&si->lock);
cond_resched();
spin_lock(&si->lock);
latency_ration = LATENCY_LIMIT;
}
/* try to get more slots in cluster */
if (si->cluster_info) {
if (scan_swap_map_try_ssd_cluster(si, &offset, &scan_base, order))
goto checks;
if (order > 0)
goto done;
} else if (si->cluster_nr && !si->swap_map[++offset]) {
/* non-ssd case, still more slots in cluster? */
--si->cluster_nr;
goto checks;
}
/*
* Even if there's no free clusters available (fragmented),
* try to scan a little more quickly with lock held unless we
* have scanned too many slots already.
*/
if (!scanned_many) {
unsigned long scan_limit;
if (offset < scan_base)
scan_limit = scan_base;
else
scan_limit = si->highest_bit;
for (; offset <= scan_limit && --latency_ration > 0;
offset++) {
if (!si->swap_map[offset])
goto checks;
}
}
done:
if (order == 0)
set_cluster_next(si, offset + 1);
si->flags -= SWP_SCANNING;
return n_ret;
scan:
VM_WARN_ON(order > 0);
spin_unlock(&si->lock);
while (++offset <= READ_ONCE(si->highest_bit)) {
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
scanned_many = true;
}
if (swap_offset_available_and_locked(si, offset))
goto checks;
}
offset = si->lowest_bit;
while (offset < scan_base) {
if (unlikely(--latency_ration < 0)) {
cond_resched();
latency_ration = LATENCY_LIMIT;
scanned_many = true;
}
if (swap_offset_available_and_locked(si, offset))
goto checks;
offset++;
}
spin_lock(&si->lock);
no_page:
si->flags -= SWP_SCANNING;
return n_ret;
}
static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
{
unsigned long offset = idx * SWAPFILE_CLUSTER;
struct swap_cluster_info *ci;
ci = lock_cluster(si, offset);
memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER);
cluster_set_count_flag(ci, 0, 0);
free_cluster(si, idx);
unlock_cluster(ci);
swap_range_free(si, offset, SWAPFILE_CLUSTER);
}
int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
{
int order = swap_entry_order(entry_order);
unsigned long size = 1 << order;
struct swap_info_struct *si, *next;
long avail_pgs;
int n_ret = 0;
int node;
spin_lock(&swap_avail_lock);
avail_pgs = atomic_long_read(&nr_swap_pages) / size;
if (avail_pgs <= 0) {
spin_unlock(&swap_avail_lock);
goto noswap;
}
n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
atomic_long_sub(n_goal * size, &nr_swap_pages);
start_over:
node = numa_node_id();
plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
/* requeue si to after same-priority siblings */
plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
spin_unlock(&swap_avail_lock);
spin_lock(&si->lock);
if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
spin_lock(&swap_avail_lock);
if (plist_node_empty(&si->avail_lists[node])) {
spin_unlock(&si->lock);
goto nextsi;
}
WARN(!si->highest_bit,
"swap_info %d in list but !highest_bit\n",
si->type);
WARN(!(si->flags & SWP_WRITEOK),
"swap_info %d in list but !SWP_WRITEOK\n",
si->type);
__del_from_avail_list(si);
spin_unlock(&si->lock);
goto nextsi;
}
n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
n_goal, swp_entries, order);
spin_unlock(&si->lock);
if (n_ret || size > 1)
goto check_out;
cond_resched();
spin_lock(&swap_avail_lock);
nextsi:
/*
* if we got here, it's likely that si was almost full before,
* and since scan_swap_map_slots() can drop the si->lock,
* 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 and taking
* si->lock. Since we dropped the swap_avail_lock, the
* swap_avail_head 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_lists[node]))
goto start_over;
}
spin_unlock(&swap_avail_lock);
check_out:
if (n_ret < n_goal)
atomic_long_add((long)(n_goal - n_ret) * size,
&nr_swap_pages);
noswap:
return n_ret;
}
static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
{
struct swap_info_struct *p;
unsigned long offset;
if (!entry.val)
goto out;
p = swp_swap_info(entry);
if (!p)
goto bad_nofile;
if (data_race(!(p->flags & SWP_USED)))
goto bad_device;
offset = swp_offset(entry);
if (offset >= p->max)
goto bad_offset;
if (data_race(!p->swap_map[swp_offset(entry)]))
goto bad_free;
return p;
bad_free:
pr_err("%s: %s%08lx\n", __func__, Unused_offset, entry.val);
goto out;
bad_offset:
pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
goto out;
bad_device:
pr_err("%s: %s%08lx\n", __func__, Unused_file, entry.val);
goto out;
bad_nofile:
pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
out:
return NULL;
}
static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry,
struct swap_info_struct *q)
{
struct swap_info_struct *p;
p = _swap_info_get(entry);
if (p != q) {
if (q != NULL)
spin_unlock(&q->lock);
if (p != NULL)
spin_lock(&p->lock);
}
return p;
}
static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
unsigned long offset,
unsigned char usage)
{
unsigned char count;
unsigned char has_cache;
count = p->swap_map[offset];
has_cache = count & SWAP_HAS_CACHE;
count &= ~SWAP_HAS_CACHE;
if (usage == SWAP_HAS_CACHE) {
VM_BUG_ON(!has_cache);
has_cache = 0;
} else if (count == SWAP_MAP_SHMEM) {
/*
* Or we could insist on shmem.c using a special
* swap_shmem_free() and free_shmem_swap_and_cache()...
*/
count = 0;
} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
if (count == COUNT_CONTINUED) {
if (swap_count_continued(p, offset, count))
count = SWAP_MAP_MAX | COUNT_CONTINUED;
else
count = SWAP_MAP_MAX;
} else
count--;
}
usage = count | has_cache;
if (usage)
WRITE_ONCE(p->swap_map[offset], usage);
else
WRITE_ONCE(p->swap_map[offset], SWAP_HAS_CACHE);
return usage;
}
/*
* 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
* __read_swap_cache_async()
* swapcache_prepare()
* __swap_duplicate()
* // 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 = swp_swap_info(entry);
if (!si)
goto bad_nofile;
if (!percpu_ref_tryget_live(&si->users))
goto out;
/*
* Guarantee the si->users are checked before accessing other
* fields of swap_info_struct.
*
* Paired with the spin_unlock() after setup_swap_info() in
* enable_swap_info().
*/
smp_rmb();
offset = swp_offset(entry);
if (offset >= si->max)
goto put_out;
return si;
bad_nofile:
pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
out:
return NULL;
put_out:
pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
percpu_ref_put(&si->users);
return NULL;
}
static unsigned char __swap_entry_free(struct swap_info_struct *p,
swp_entry_t entry)
{
struct swap_cluster_info *ci;
unsigned long offset = swp_offset(entry);
unsigned char usage;
ci = lock_cluster_or_swap_info(p, offset);
usage = __swap_entry_free_locked(p, offset, 1);
unlock_cluster_or_swap_info(p, ci);
if (!usage)
free_swap_slot(entry);
return usage;
}
static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
{
struct swap_cluster_info *ci;
unsigned long offset = swp_offset(entry);
unsigned char count;
ci = lock_cluster(p, offset);
count = p->swap_map[offset];
VM_BUG_ON(count != SWAP_HAS_CACHE);
p->swap_map[offset] = 0;
dec_cluster_info_page(p, p->cluster_info, offset);
unlock_cluster(ci);
mem_cgroup_uncharge_swap(entry, 1);
swap_range_free(p, offset, 1);
}
/*
* Caller has made sure that the swap device corresponding to entry
* is still around or has not been recycled.
*/
void swap_free(swp_entry_t entry)
{
struct swap_info_struct *p;
p = _swap_info_get(entry);
if (p)
__swap_entry_free(p, entry);
}
/*
* Called after dropping swapcache to decrease refcnt to swap entries.
*/
void put_swap_folio(struct folio *folio, swp_entry_t entry)
{
unsigned long offset = swp_offset(entry);
unsigned long idx = offset / SWAPFILE_CLUSTER;
struct swap_cluster_info *ci;
struct swap_info_struct *si;
unsigned char *map;
unsigned int i, free_entries = 0;
unsigned char val;
int size = 1 << swap_entry_order(folio_order(folio));
si = _swap_info_get(entry);
if (!si)
return;
ci = lock_cluster_or_swap_info(si, offset);
if (size == SWAPFILE_CLUSTER) {
map = si->swap_map + offset;
for (i = 0; i < SWAPFILE_CLUSTER; i++) {
val = map[i];
VM_BUG_ON(!(val & SWAP_HAS_CACHE));
if (val == SWAP_HAS_CACHE)
free_entries++;
}
if (free_entries == SWAPFILE_CLUSTER) {
unlock_cluster_or_swap_info(si, ci);
spin_lock(&si->lock);
mem_cgroup_uncharge_swap(entry, SWAPFILE_CLUSTER);
swap_free_cluster(si, idx);
spin_unlock(&si->lock);
return;
}
}
for (i = 0; i < size; i++, entry.val++) {
if (!__swap_entry_free_locked(si, offset + i, SWAP_HAS_CACHE)) {
unlock_cluster_or_swap_info(si, ci);
free_swap_slot(entry);
if (i == size - 1)
return;
lock_cluster_or_swap_info(si, offset);
}
}
unlock_cluster_or_swap_info(si, ci);
}
static int swp_entry_cmp(const void *ent1, const void *ent2)
{
const swp_entry_t *e1 = ent1, *e2 = ent2;
return (int)swp_type(*e1) - (int)swp_type(*e2);
}
void swapcache_free_entries(swp_entry_t *entries, int n)
{
struct swap_info_struct *p, *prev;
int i;
if (n <= 0)
return;
prev = NULL;
p = NULL;
/*
* Sort swap entries by swap device, so each lock is only taken once.
* nr_swapfiles isn't absolutely correct, but the overhead of sort() is
* so low that it isn't necessary to optimize further.
*/
if (nr_swapfiles > 1)
sort(entries, n, sizeof(entries[0]), swp_entry_cmp, NULL);
for (i = 0; i < n; ++i) {
p = swap_info_get_cont(entries[i], prev);
if (p)
swap_entry_free(p, entries[i]);
prev = p;
}
if (p)
spin_unlock(&p->lock);
}
int __swap_count(swp_entry_t entry)
{
struct swap_info_struct *si = swp_swap_info(entry);
pgoff_t offset = swp_offset(entry);
return swap_count(si->swap_map[offset]);
}
/*
* How many references to @entry are currently swapped out?
* This does not give an exact answer when swap count is continued,
* but does include the high COUNT_CONTINUED flag to allow for that.
*/
int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
{
pgoff_t offset = swp_offset(entry);
struct swap_cluster_info *ci;
int count;
ci = lock_cluster_or_swap_info(si, offset);
count = swap_count(si->swap_map[offset]);
unlock_cluster_or_swap_info(si, ci);
return count;
}
/*
* How many references to @entry are currently swapped out?
* This considers COUNT_CONTINUED so it returns exact answer.
*/
int swp_swapcount(swp_entry_t entry)
{
int count, tmp_count, n;
struct swap_info_struct *p;
struct swap_cluster_info *ci;
struct page *page;
pgoff_t offset;
unsigned char *map;
p = _swap_info_get(entry);
if (!p)
return 0;
offset = swp_offset(entry);
ci = lock_cluster_or_swap_info(p, offset);
count = swap_count(p->swap_map[offset]);
if (!(count & COUNT_CONTINUED))
goto out;
count &= ~COUNT_CONTINUED;
n = SWAP_MAP_MAX + 1;
page = vmalloc_to_page(p->swap_map + offset);
offset &= ~PAGE_MASK;
VM_BUG_ON(page_private(page) != SWP_CONTINUED);
do {
page = list_next_entry(page, lru);
map = kmap_local_page(page);
tmp_count = map[offset];
kunmap_local(map);
count += (tmp_count & ~COUNT_CONTINUED) * n;
n *= (SWAP_CONT_MAX + 1);
} while (tmp_count & COUNT_CONTINUED);
out:
unlock_cluster_or_swap_info(p, ci);
return count;
}
static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
swp_entry_t entry, int order)
{
struct swap_cluster_info *ci;
unsigned char *map = si->swap_map;
unsigned int nr_pages = 1 << order;
unsigned long roffset = swp_offset(entry);
unsigned long offset = round_down(roffset, nr_pages);
int i;
bool ret = false;
ci = lock_cluster_or_swap_info(si, offset);
if (!ci || nr_pages == 1) {
if (swap_count(map[roffset]))
ret = true;
goto unlock_out;
}
for (i = 0; i < nr_pages; i++) {
if (swap_count(map[offset + i])) {
ret = true;
break;
}
}
unlock_out:
unlock_cluster_or_swap_info(si, ci);
return ret;
}
static bool folio_swapped(struct folio *folio)
{
swp_entry_t entry = folio->swap;
struct swap_info_struct *si = _swap_info_get(entry);
if (!si)
return false;
if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!folio_test_large(folio)))
return swap_swapcount(si, entry) != 0;
return swap_page_trans_huge_swapped(si, entry, folio_order(folio));
}
/**
* 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)
{
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
if (!folio_test_swapcache(folio))
return false;
if (folio_test_writeback(folio))
return false;
if (folio_swapped(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;
delete_from_swap_cache(folio);
folio_set_dirty(folio);
return true;
}
/**
* free_swap_and_cache_nr() - 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).
*/
void free_swap_and_cache_nr(swp_entry_t entry, int nr)
{
const unsigned long start_offset = swp_offset(entry);
const unsigned long end_offset = start_offset + nr;
unsigned int type = swp_type(entry);
struct swap_info_struct *si;
bool any_only_cache = false;
unsigned long offset;
unsigned char count;
if (non_swap_entry(entry))
return;
si = get_swap_device(entry);
if (!si)
return;
if (WARN_ON(end_offset > si->max))
goto out;
/*
* First free all entries in the range.
*/
for (offset = start_offset; offset < end_offset; offset++) {
if (data_race(si->swap_map[offset])) {
count = __swap_entry_free(si, swp_entry(type, offset));
if (count == SWAP_HAS_CACHE)
any_only_cache = true;
} else {
WARN_ON_ONCE(1);
}
}
/*
* Short-circuit the below loop if none of the entries had their
* reference drop to zero.
*/
if (!any_only_cache)
goto out;
/*
* Now go back over the range trying to reclaim the swap cache. This is
* more efficient for large folios because we will only try to reclaim
* the swap once per folio in the common case. If we do
* __swap_entry_free() and __try_to_reclaim_swap() in the same loop, the
* latter will get a reference and lock the folio for every individual
* page but will only succeed once the swap slot for every subpage is
* zero.
*/
for (offset = start_offset; offset < end_offset; offset += nr) {
nr = 1;
if (READ_ONCE(si->swap_map[offset]) == SWAP_HAS_CACHE) {
/*
* Folios are always naturally aligned in swap so
* advance forward to the next boundary. Zero means no
* folio was found for the swap entry, so advance by 1
* in this case. Negative value means folio was found
* but could not be reclaimed. Here we can still advance
* to the next boundary.
*/
nr = __try_to_reclaim_swap(si, offset,
TTRS_UNMAPPED | TTRS_FULL);
if (nr == 0)
nr = 1;
else if (nr < 0)
nr = -nr;
nr = ALIGN(offset + 1, nr) - offset;
}
}
out:
put_swap_device(si);
}
#ifdef CONFIG_HIBERNATION
swp_entry_t get_swap_page_of_type(int type)
{
struct swap_info_struct *si = swap_type_to_swap_info(type);
swp_entry_t entry = {0};
if (!si)
goto fail;
/* This is called for allocating swap entry, not cache */
spin_lock(&si->lock);
if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry, 0))
atomic_long_dec(&nr_swap_pages);
spin_unlock(&si->lock);
fail:
return entry;
}
/*
* Find the swap type that corresponds to given device (if any).
*
* @offset - number of the PAGE_SIZE-sized block of the device, starting
* from 0, in which the swap header is expected to be located.
*
* This is needed for the suspend to disk (aka swsusp).
*/
int swap_type_of(dev_t device, sector_t offset)
{
int type;
if (!device)
return -1;
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;
if (device == sis->bdev->bd_dev) {
struct swap_extent *se = first_se(sis);
if (se->start_block == offset) {
spin_unlock(&swap_lock);
return type;
}
}
}
spin_unlock(&swap_lock);
return -ENODEV;
}
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_swap_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 -= sis->inuse_pages;
}
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;
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 swap_free().
*/
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;
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);
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_wp(old_pte))
new_pte = pte_mkuffd_wp(new_pte);
setpte:
set_pte_at(vma->vm_mm, addr, pte, new_pte);
swap_free(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;
struct swap_info_struct *si;
si = swap_info[type];
do {
struct folio *folio;
unsigned long offset;
unsigned char swp_count;
swp_entry_t entry;
int ret;
pte_t ptent;
if (!pte++) {
pte = pte_offset_map(pmd, addr);
if (!pte)
break;
}
ptent = ptep_get_lockless(pte);
if (!is_swap_pte(ptent))
continue;
entry = pte_to_swp_entry(ptent);
if (swp_type(entry) != type)
continue;
offset = swp_offset(entry);
pte_unmap(pte);
pte = NULL;
folio = swap_cache_get_folio(entry, vma, addr);
if (!folio) {
struct page *page;
struct vm_fault vmf = {
.vma = vma,
.address = addr,
.real_address = addr,
.pmd = pmd,
};
page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
&vmf);
if (page)
folio = page_folio(page);
}
if (!folio) {
swp_count = READ_ONCE(si->swap_map[offset]);
if (swp_count == 0 || swp_count == SWAP_MAP_BAD)
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);
for_each_vma(vmi, vma) {
if (vma->anon_vma) {
ret = unuse_vma(vma, type);
if (ret)
break;
}
cond_resched();
}
mmap_read_unlock(mm);
return ret;
}
/*
* Scan swap_map 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 char count;
/*
* 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++) {
count = READ_ONCE(si->swap_map[i]);
if (count && swap_count(count) != SWAP_MAP_BAD)
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 (!READ_ONCE(si->inuse_pages))
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 (READ_ONCE(si->inuse_pages) &&
!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 (READ_ONCE(si->inuse_pages) &&
!signal_pending(current) &&
(i = find_next_to_unuse(si, i)) != 0) {
entry = swp_entry(type, i);
folio = filemap_get_folio(swap_address_space(entry), i);
if (IS_ERR(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_writepage() 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 (READ_ONCE(si->inuse_pages)) {
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_info[type]->inuse_pages)
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)
{
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 file *swap_file = sis->swap_file;
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(sizeof(*se), GFP_KERNEL);
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, sector_t *span)
{
struct file *swap_file = sis->swap_file;
struct address_space *mapping = swap_file->f_mapping;
struct inode *inode = mapping->host;
int ret;
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;
if ((sis->flags & SWP_FS_OPS) &&
sio_pool_init() != 0) {
destroy_swap_extents(sis);
return -ENOMEM;
}
return ret;
}
return generic_swapfile_activate(sis, swap_file, span);
}
static int swap_node(struct swap_info_struct *p)
{
struct block_device *bdev;
if (p->bdev)
bdev = p->bdev;
else
bdev = p->swap_file->f_inode->i_sb->s_bdev;
return bdev ? bdev->bd_disk->node_id : NUMA_NO_NODE;
}
static void setup_swap_info(struct swap_info_struct *p, int prio,
unsigned char *swap_map,
struct swap_cluster_info *cluster_info)
{
int i;
if (prio >= 0)
p->prio = prio;
else
p->prio = --least_priority;
/*
* the plist prio is negated because plist ordering is
* low-to-high, while swap ordering is high-to-low
*/
p->list.prio = -p->prio;
for_each_node(i) {
if (p->prio >= 0)
p->avail_lists[i].prio = -p->prio;
else {
if (swap_node(p) == i)
p->avail_lists[i].prio = 1;
else
p->avail_lists[i].prio = -p->prio;
}
}
p->swap_map = swap_map;
p->cluster_info = cluster_info;
}
static void _enable_swap_info(struct swap_info_struct *p)
{
p->flags |= SWP_WRITEOK;
atomic_long_add(p->pages, &nr_swap_pages);
total_swap_pages += p->pages;
assert_spin_locked(&swap_lock);
/*
* both lists are plists, and thus priority ordered.
* swap_active_head needs to be priority ordered for swapoff(),
* which on removal of any swap_info_struct with an auto-assigned
* (i.e. negative) priority increments the auto-assigned priority
* of any lower-priority swap_info_structs.
* swap_avail_head needs to be priority ordered for folio_alloc_swap(),
* which allocates swap pages from the highest available priority
* swap_info_struct.
*/
plist_add(&p->list, &swap_active_head);
/* add to available list iff swap device is not full */
if (p->highest_bit)
add_to_avail_list(p);
}
static void enable_swap_info(struct swap_info_struct *p, int prio,
unsigned char *swap_map,
struct swap_cluster_info *cluster_info)
{
spin_lock(&swap_lock);
spin_lock(&p->lock);
setup_swap_info(p, prio, swap_map, cluster_info);
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
/*
* Finished initializing swap device, now it's safe to reference it.
*/
percpu_ref_resurrect(&p->users);
spin_lock(&swap_lock);
spin_lock(&p->lock);
_enable_swap_info(p);
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
}
static void reinsert_swap_info(struct swap_info_struct *p)
{
spin_lock(&swap_lock);
spin_lock(&p->lock);
setup_swap_info(p, p->prio, p->swap_map, p->cluster_info);
_enable_swap_info(p);
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
}
bool has_usable_swap(void)
{
bool ret = true;
spin_lock(&swap_lock);
if (plist_head_empty(&swap_active_head))
ret = false;
spin_unlock(&swap_lock);
return ret;
}
SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
{
struct swap_info_struct *p = NULL;
unsigned char *swap_map;
struct swap_cluster_info *cluster_info;
struct file *swap_file, *victim;
struct address_space *mapping;
struct inode *inode;
struct filename *pathname;
int err, found = 0;
unsigned int old_block_size;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
BUG_ON(!current->mm);
pathname = getname(specialfile);
if (IS_ERR(pathname))
return PTR_ERR(pathname);
victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
err = PTR_ERR(victim);
if (IS_ERR(victim))
goto out;
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;
}
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);
if (p->prio < 0) {
struct swap_info_struct *si = p;
int nid;
plist_for_each_entry_continue(si, &swap_active_head, list) {
si->prio++;
si->list.prio--;
for_each_node(nid) {
if (si->avail_lists[nid].prio != 1)
si->avail_lists[nid].prio--;
}
}
least_priority++;
}
plist_del(&p->list, &swap_active_head);
atomic_long_sub(p->pages, &nr_swap_pages);
total_swap_pages -= p->pages;
p->flags &= ~SWP_WRITEOK;
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
disable_swap_slots_cache_lock();
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);
reenable_swap_slots_cache_unlock();
goto out_dput;
}
reenable_swap_slots_cache_unlock();
/*
* 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);
destroy_swap_extents(p);
if (p->flags & SWP_CONTINUED)
free_swap_count_continuations(p);
if (!p->bdev || !bdev_nonrot(p->bdev))
atomic_dec(&nr_rotate_swap);
mutex_lock(&swapon_mutex);
spin_lock(&swap_lock);
spin_lock(&p->lock);
drain_mmlist();
/* wait for anyone still in scan_swap_map_slots */
p->highest_bit = 0; /* cuts scans short */
while (p->flags >= SWP_SCANNING) {
spin_unlock(&p->lock);
spin_unlock(&swap_lock);
schedule_timeout_uninterruptible(1);
spin_lock(&swap_lock);
spin_lock(&p->lock);
}
swap_file = p->swap_file;
old_block_size = p->old_block_size;
p->swap_file = NULL;
p->max = 0;
swap_map = p->swap_map;
p->swap_map = NULL;
cluster_info = p->cluster_info;
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);
free_percpu(p->percpu_cluster);
p->percpu_cluster = NULL;
free_percpu(p->cluster_next_cpu);
p->cluster_next_cpu = NULL;
vfree(swap_map);
kvfree(cluster_info);
/* Destroy swap account information */
swap_cgroup_swapoff(p->type);
exit_swap_address_space(p->type);
inode = mapping->host;
if (p->bdev_file) {
set_blocksize(p->bdev, old_block_size);
fput(p->bdev_file);
p->bdev_file = NULL;
}
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);
out:
putname(pathname);
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_swap_info(type)); type++) {
if (!(si->flags & SWP_USED) || !si->swap_map)
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_swap_info(type)); type++) {
if (!(si->flags & SWP_USED) || !si->swap_map)
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(READ_ONCE(si->inuse_pages));
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;
int i;
p = kvzalloc(struct_size(p, avail_lists, nr_node_ids), GFP_KERNEL);
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);
for_each_node(i)
plist_node_init(&p->avail_lists[i], 0);
p->flags = SWP_USED;
spin_unlock(&swap_lock);
if (defer) {
percpu_ref_exit(&defer->users);
kvfree(defer);
}
spin_lock_init(&p->lock);
spin_lock_init(&p->cont_lock);
init_completion(&p->comp);
return p;
}
static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
{
int error;
if (S_ISBLK(inode->i_mode)) {
p->bdev_file = bdev_file_open_by_dev(inode->i_rdev,
BLK_OPEN_READ | BLK_OPEN_WRITE, p, NULL);
if (IS_ERR(p->bdev_file)) {
error = PTR_ERR(p->bdev_file);
p->bdev_file = NULL;
return error;
}
p->bdev = file_bdev(p->bdev_file);
p->old_block_size = block_size(p->bdev);
error = set_blocksize(p->bdev, PAGE_SIZE);
if (error < 0)
return error;
/*
* 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(p->bdev))
return -EINVAL;
p->flags |= SWP_BLKDEV;
} else if (S_ISREG(inode->i_mode)) {
p->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)
{
return swp_offset(pte_to_swp_entry(
swp_entry_to_pte(swp_entry(0, ~0UL)))) + 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 *p,
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;
}
p->lowest_bit = 1;
p->cluster_next = 1;
p->cluster_nr = 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;
}
p->highest_bit = maxpages - 1;
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;
}
#define SWAP_CLUSTER_INFO_COLS \
DIV_ROUND_UP(L1_CACHE_BYTES, sizeof(struct swap_cluster_info))
#define SWAP_CLUSTER_SPACE_COLS \
DIV_ROUND_UP(SWAP_ADDRESS_SPACE_PAGES, SWAPFILE_CLUSTER)
#define SWAP_CLUSTER_COLS \
max_t(unsigned int, SWAP_CLUSTER_INFO_COLS, SWAP_CLUSTER_SPACE_COLS)
static int setup_swap_map_and_extents(struct swap_info_struct *p,
union swap_header *swap_header,
unsigned char *swap_map,
struct swap_cluster_info *cluster_info,
unsigned long maxpages,
sector_t *span)
{
unsigned int j, k;
unsigned int nr_good_pages;
int nr_extents;
unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
unsigned long col = p->cluster_next / SWAPFILE_CLUSTER % SWAP_CLUSTER_COLS;
unsigned long i, idx;
nr_good_pages = maxpages - 1; /* omit header page */
cluster_list_init(&p->free_clusters);
cluster_list_init(&p->discard_clusters);
for (i = 0; i < swap_header->info.nr_badpages; i++) {
unsigned int page_nr = swap_header->info.badpages[i];
if (page_nr == 0 || page_nr > swap_header->info.last_page)
return -EINVAL;
if (page_nr < maxpages) {
swap_map[page_nr] = SWAP_MAP_BAD;
nr_good_pages--;
/*
* Haven't marked the cluster free yet, no list
* operation involved
*/
inc_cluster_info_page(p, cluster_info, page_nr);
}
}
/* Haven't marked the cluster free yet, no list operation involved */
for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
inc_cluster_info_page(p, cluster_info, i);
if (nr_good_pages) {
swap_map[0] = SWAP_MAP_BAD;
/*
* Not mark the cluster free yet, no list
* operation involved
*/
inc_cluster_info_page(p, cluster_info, 0);
p->max = maxpages;
p->pages = nr_good_pages;
nr_extents = setup_swap_extents(p, span);
if (nr_extents < 0)
return nr_extents;
nr_good_pages = p->pages;
}
if (!nr_good_pages) {
pr_warn("Empty swap-file\n");
return -EINVAL;
}
if (!cluster_info)
return nr_extents;
/*
* Reduce false cache line sharing between cluster_info and
* sharing same address space.
*/
for (k = 0; k < SWAP_CLUSTER_COLS; k++) {
j = (k + col) % SWAP_CLUSTER_COLS;
for (i = 0; i < DIV_ROUND_UP(nr_clusters, SWAP_CLUSTER_COLS); i++) {
idx = i * SWAP_CLUSTER_COLS + j;
if (idx >= nr_clusters)
continue;
if (cluster_count(&cluster_info[idx]))
continue;
cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
cluster_list_add_tail(&p->free_clusters, cluster_info,
idx);
}
}
return nr_extents;
}
SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
{
struct swap_info_struct *p;
struct filename *name;
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;
unsigned char *swap_map = NULL;
struct swap_cluster_info *cluster_info = NULL;
struct page *page = 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;
if (!swap_avail_heads)
return -ENOMEM;
p = alloc_swap_info();
if (IS_ERR(p))
return PTR_ERR(p);
INIT_WORK(&p->discard_work, swap_discard_work);
name = getname(specialfile);
if (IS_ERR(name)) {
error = PTR_ERR(name);
name = NULL;
goto bad_swap;
}
swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
if (IS_ERR(swap_file)) {
error = PTR_ERR(swap_file);
swap_file = NULL;
goto bad_swap;
}
p->swap_file = swap_file;
mapping = swap_file->f_mapping;
dentry = swap_file->f_path.dentry;
inode = mapping->host;
error = claim_swapfile(p, 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;
}
/*
* Read the swap header.
*/
if (!mapping->a_ops->read_folio) {
error = -EINVAL;
goto bad_swap_unlock_inode;
}
page = read_mapping_page(mapping, 0, swap_file);
if (IS_ERR(page)) {
error = PTR_ERR(page);
goto bad_swap_unlock_inode;
}
swap_header = kmap(page);
maxpages = read_swap_header(p, swap_header, inode);
if (unlikely(!maxpages)) {
error = -EINVAL;
goto bad_swap_unlock_inode;
}
/* OK, set up the swap map and apply the bad block list */
swap_map = vzalloc(maxpages);
if (!swap_map) {
error = -ENOMEM;
goto bad_swap_unlock_inode;
}
if (p->bdev && bdev_stable_writes(p->bdev))
p->flags |= SWP_STABLE_WRITES;
if (p->bdev && bdev_synchronous(p->bdev))
p->flags |= SWP_SYNCHRONOUS_IO;
if (p->bdev && bdev_nonrot(p->bdev)) {
int cpu, i;
unsigned long ci, nr_cluster;
p->flags |= SWP_SOLIDSTATE;
p->cluster_next_cpu = alloc_percpu(unsigned int);
if (!p->cluster_next_cpu) {
error = -ENOMEM;
goto bad_swap_unlock_inode;
}
/*
* select a random position to start with to help wear leveling
* SSD
*/
for_each_possible_cpu(cpu) {
per_cpu(*p->cluster_next_cpu, cpu) =
get_random_u32_inclusive(1, p->highest_bit);
}
nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info),
GFP_KERNEL);
if (!cluster_info) {
error = -ENOMEM;
goto bad_swap_unlock_inode;
}
for (ci = 0; ci < nr_cluster; ci++)
spin_lock_init(&((cluster_info + ci)->lock));
p->percpu_cluster = alloc_percpu(struct percpu_cluster);
if (!p->percpu_cluster) {
error = -ENOMEM;
goto bad_swap_unlock_inode;
}
for_each_possible_cpu(cpu) {
struct percpu_cluster *cluster;
cluster = per_cpu_ptr(p->percpu_cluster, cpu);
for (i = 0; i < SWAP_NR_ORDERS; i++)
cluster->next[i] = SWAP_NEXT_INVALID;
}
} else {
atomic_inc(&nr_rotate_swap);
inced_nr_rotate_swap = true;
}
error = swap_cgroup_swapon(p->type, maxpages);
if (error)
goto bad_swap_unlock_inode;
nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
cluster_info, maxpages, &span);
if (unlikely(nr_extents < 0)) {
error = nr_extents;
goto bad_swap_unlock_inode;
}
if ((swap_flags & SWAP_FLAG_DISCARD) &&
p->bdev && bdev_max_discard_sectors(p->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.
*/
p->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)
p->flags &= ~SWP_PAGE_DISCARD;
else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
p->flags &= ~SWP_AREA_DISCARD;
/* issue a swapon-time discard if it's still required */
if (p->flags & SWP_AREA_DISCARD) {
int err = discard_swap(p);
if (unlikely(err))
pr_err("swapon: discard_swap(%p): %d\n",
p, err);
}
}
error = init_swap_address_space(p->type, maxpages);
if (error)
goto bad_swap_unlock_inode;
error = zswap_swapon(p->type, maxpages);
if (error)
goto free_swap_address_space;
/*
* 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 = -1;
if (swap_flags & SWAP_FLAG_PREFER)
prio =
(swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
enable_swap_info(p, prio, swap_map, cluster_info);
pr_info("Adding %uk swap on %s. Priority:%d extents:%d across:%lluk %s%s%s%s\n",
K(p->pages), name->name, p->prio, nr_extents,
K((unsigned long long)span),
(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
(p->flags & SWP_DISCARDABLE) ? "D" : "",
(p->flags & SWP_AREA_DISCARD) ? "s" : "",
(p->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(p->type);
free_swap_address_space:
exit_swap_address_space(p->type);
bad_swap_unlock_inode:
inode_unlock(inode);
bad_swap:
free_percpu(p->percpu_cluster);
p->percpu_cluster = NULL;
free_percpu(p->cluster_next_cpu);
p->cluster_next_cpu = NULL;
if (p->bdev_file) {
set_blocksize(p->bdev, p->old_block_size);
fput(p->bdev_file);
p->bdev_file = NULL;
}
inode = NULL;
destroy_swap_extents(p);
swap_cgroup_swapoff(p->type);
spin_lock(&swap_lock);
p->swap_file = NULL;
p->flags = 0;
spin_unlock(&swap_lock);
vfree(swap_map);
kvfree(cluster_info);
if (inced_nr_rotate_swap)
atomic_dec(&nr_rotate_swap);
if (swap_file)
filp_close(swap_file, NULL);
out:
if (page && !IS_ERR(page)) {
kunmap(page);
put_page(page);
}
if (name)
putname(name);
if (inode)
inode_unlock(inode);
if (!error)
enable_swap_slots_cache();
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 += READ_ONCE(si->inuse_pages);
}
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);
}
/*
* Verify that a swap entry is valid and increment its swap map count.
*
* Returns error code in following case.
* - success -> 0
* - swp_entry is invalid -> EINVAL
* - swp_entry is migration entry -> EINVAL
* - swap-cache reference is requested but there is already one. -> EEXIST
* - swap-cache reference is requested but the entry is not used. -> ENOENT
* - swap-mapped reference requested but needs continued swap count. -> ENOMEM
*/
static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
{
struct swap_info_struct *p;
struct swap_cluster_info *ci;
unsigned long offset;
unsigned char count;
unsigned char has_cache;
int err;
p = swp_swap_info(entry);
offset = swp_offset(entry);
ci = lock_cluster_or_swap_info(p, offset);
count = p->swap_map[offset];
/*
* swapin_readahead() doesn't check if a swap entry is valid, so the
* swap entry could be SWAP_MAP_BAD. Check here with lock held.
*/
if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
err = -ENOENT;
goto unlock_out;
}
has_cache = count & SWAP_HAS_CACHE;
count &= ~SWAP_HAS_CACHE;
err = 0;
if (usage == SWAP_HAS_CACHE) {
/* set SWAP_HAS_CACHE if there is no cache and entry is used */
if (!has_cache && count)
has_cache = SWAP_HAS_CACHE;
else if (has_cache) /* someone else added cache */
err = -EEXIST;
else /* no users remaining */
err = -ENOENT;
} else if (count || has_cache) {
if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
count += usage;
else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
err = -EINVAL;
else if (swap_count_continued(p, offset, count))
count = COUNT_CONTINUED;
else
err = -ENOMEM;
} else
err = -ENOENT; /* unused swap entry */
if (!err)
WRITE_ONCE(p->swap_map[offset], count | has_cache);
unlock_out:
unlock_cluster_or_swap_info(p, ci);
return err;
}
/*
* Help swapoff by noting that swap entry belongs to shmem/tmpfs
* (in which case its reference count is never incremented).
*/
void swap_shmem_alloc(swp_entry_t entry)
{
__swap_duplicate(entry, SWAP_MAP_SHMEM);
}
/*
* Increase reference count of swap entry by 1.
* Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
* but could not be atomically allocated. Returns 0, just as if it succeeded,
* if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
* might occur if a page table entry has got corrupted.
*/
int swap_duplicate(swp_entry_t entry)
{
int err = 0;
while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
err = add_swap_count_continuation(entry, GFP_ATOMIC);
return err;
}
/*
* @entry: swap entry for which we allocate swap cache.
*
* Called when allocating swap cache for existing swap entry,
* This can return error codes. Returns 0 at success.
* -EEXIST means there is a swap cache.
* Note: return code is different from swap_duplicate().
*/
int swapcache_prepare(swp_entry_t entry)
{
return __swap_duplicate(entry, SWAP_HAS_CACHE);
}
void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry)
{
struct swap_cluster_info *ci;
unsigned long offset = swp_offset(entry);
unsigned char usage;
ci = lock_cluster_or_swap_info(si, offset);
usage = __swap_entry_free_locked(si, offset, SWAP_HAS_CACHE);
unlock_cluster_or_swap_info(si, ci);
if (!usage)
free_swap_slot(entry);
}
struct swap_info_struct *swp_swap_info(swp_entry_t entry)
{
return swap_type_to_swap_info(swp_type(entry));
}
/*
* out-of-line methods to avoid include hell.
*/
struct address_space *swapcache_mapping(struct folio *folio)
{
return swp_swap_info(folio->swap)->swap_file->f_mapping;
}
EXPORT_SYMBOL_GPL(swapcache_mapping);
pgoff_t __page_file_index(struct page *page)
{
swp_entry_t swap = page_swap_entry(page);
return swp_offset(swap);
}
EXPORT_SYMBOL_GPL(__page_file_index);
/*
* add_swap_count_continuation - called when a swap count is duplicated
* beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
* page of the original vmalloc'ed swap_map, to hold the continuation count
* (for that entry and for its neighbouring PAGE_SIZE swap entries). Called
* again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
*
* These continuation pages are seldom referenced: the common paths all work
* on the original swap_map, only referring to a continuation page when the
* low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
*
* add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
* page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
* can be called after dropping locks.
*/
int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
{
struct swap_info_struct *si;
struct swap_cluster_info *ci;
struct page *head;
struct page *page;
struct page *list_page;
pgoff_t offset;
unsigned char count;
int ret = 0;
/*
* When debugging, it's easier to use __GFP_ZERO here; but it's better
* for latency not to zero a page while GFP_ATOMIC and holding locks.
*/
page = alloc_page(gfp_mask | __GFP_HIGHMEM);
si = get_swap_device(entry);
if (!si) {
/*
* An acceptable race has occurred since the failing
* __swap_duplicate(): the swap device may be swapoff
*/
goto outer;
}
spin_lock(&si->lock);
offset = swp_offset(entry);
ci = lock_cluster(si, offset);
count = swap_count(si->swap_map[offset]);
if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
/*
* The higher the swap count, the more likely it is that tasks
* will race to add swap count continuation: we need to avoid
* over-provisioning.
*/
goto out;
}
if (!page) {
ret = -ENOMEM;
goto out;
}
head = vmalloc_to_page(si->swap_map + offset);
offset &= ~PAGE_MASK;
spin_lock(&si->cont_lock);
/*
* Page allocation does not initialize the page's lru field,
* but it does always reset its private field.
*/
if (!page_private(head)) {
BUG_ON(count & COUNT_CONTINUED);
INIT_LIST_HEAD(&head->lru);
set_page_private(head, SWP_CONTINUED);
si->flags |= SWP_CONTINUED;
}
list_for_each_entry(list_page, &head->lru, lru) {
unsigned char *map;
/*
* If the previous map said no continuation, but we've found
* a continuation page, free our allocation and use this one.
*/
if (!(count & COUNT_CONTINUED))
goto out_unlock_cont;
map = kmap_local_page(list_page) + offset;
count = *map;
kunmap_local(map);
/*
* If this continuation count now has some space in it,
* free our allocation and use this one.
*/
if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
goto out_unlock_cont;
}
list_add_tail(&page->lru, &head->lru);
page = NULL; /* now it's attached, don't free it */
out_unlock_cont:
spin_unlock(&si->cont_lock);
out:
unlock_cluster(ci);
spin_unlock(&si->lock);
put_swap_device(si);
outer:
if (page)
__free_page(page);
return ret;
}
/*
* swap_count_continued - when the original swap_map count is incremented
* from SWAP_MAP_MAX, check if there is already a continuation page to carry
* into, carry if so, or else fail until a new continuation page is allocated;
* when the original swap_map count is decremented from 0 with continuation,
* borrow from the continuation and report whether it still holds more.
* Called while __swap_duplicate() or swap_entry_free() holds swap or cluster
* lock.
*/
static bool swap_count_continued(struct swap_info_struct *si,
pgoff_t offset, unsigned char count)
{
struct page *head;
struct page *page;
unsigned char *map;
bool ret;
head = vmalloc_to_page(si->swap_map + offset);
if (page_private(head) != SWP_CONTINUED) {
BUG_ON(count & COUNT_CONTINUED);
return false; /* need to add count continuation */
}
spin_lock(&si->cont_lock);
offset &= ~PAGE_MASK;
page = list_next_entry(head, lru);
map = kmap_local_page(page) + offset;
if (count == SWAP_MAP_MAX) /* initial increment from swap_map */
goto init_map; /* jump over SWAP_CONT_MAX checks */
if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
/*
* Think of how you add 1 to 999
*/
while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
kunmap_local(map);
page = list_next_entry(page, lru);
BUG_ON(page == head);
map = kmap_local_page(page) + offset;
}
if (*map == SWAP_CONT_MAX) {
kunmap_local(map);
page = list_next_entry(page, lru);
if (page == head) {
ret = false; /* add count continuation */
goto out;
}
map = kmap_local_page(page) + offset;
init_map: *map = 0; /* we didn't zero the page */
}
*map += 1;
kunmap_local(map);
while ((page = list_prev_entry(page, lru)) != head) {
map = kmap_local_page(page) + offset;
*map = COUNT_CONTINUED;
kunmap_local(map);
}
ret = true; /* incremented */
} else { /* decrementing */
/*
* Think of how you subtract 1 from 1000
*/
BUG_ON(count != COUNT_CONTINUED);
while (*map == COUNT_CONTINUED) {
kunmap_local(map);
page = list_next_entry(page, lru);
BUG_ON(page == head);
map = kmap_local_page(page) + offset;
}
BUG_ON(*map == 0);
*map -= 1;
if (*map == 0)
count = 0;
kunmap_local(map);
while ((page = list_prev_entry(page, lru)) != head) {
map = kmap_local_page(page) + offset;
*map = SWAP_CONT_MAX | count;
count = COUNT_CONTINUED;
kunmap_local(map);
}
ret = count == COUNT_CONTINUED;
}
out:
spin_unlock(&si->cont_lock);
return ret;
}
/*
* free_swap_count_continuations - swapoff free all the continuation pages
* appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
*/
static void free_swap_count_continuations(struct swap_info_struct *si)
{
pgoff_t offset;
for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
struct page *head;
head = vmalloc_to_page(si->swap_map + offset);
if (page_private(head)) {
struct page *page, *next;
list_for_each_entry_safe(page, next, &head->lru, lru) {
list_del(&page->lru);
__free_page(page);
}
}
}
}
#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
void __folio_throttle_swaprate(struct folio *folio, gfp_t gfp)
{
struct swap_info_struct *si, *next;
int nid = folio_nid(folio);
if (!(gfp & __GFP_IO))
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_safe(si, next, &swap_avail_heads[nid],
avail_lists[nid]) {
if (si->bdev) {
blkcg_schedule_throttle(si->bdev->bd_disk, true);
break;
}
}
spin_unlock(&swap_avail_lock);
}
#endif
static int __init swapfile_init(void)
{
int nid;
swap_avail_heads = kmalloc_array(nr_node_ids, sizeof(struct plist_head),
GFP_KERNEL);
if (!swap_avail_heads) {
pr_emerg("Not enough memory for swap heads, swap is disabled\n");
return -ENOMEM;
}
for_each_node(nid)
plist_head_init(&swap_avail_heads[nid]);
swapfile_maximum_size = arch_max_swapfile_size();
#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);
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