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mm: swap: allow cache reclaim to skip slot cache

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Currently we free the reclaimed slots through slot cache even if the slot
is required to be empty immediately.  As a result the reclaim caller will
see the slot still occupied even after a successful reclaim, and need to
keep reclaiming until slot cache get flushed.  This caused ineffective or
over reclaim when SWAP is under stress.

So introduce a new flag allowing the slot to be emptied bypassing the slot
cache.

[21cnbao@gmail.com: small folios should have nr_pages == 1 but not nr_page == 0]
  Link: https://lkml.kernel.org/r/20240805015324.45134-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20240730-swap-allocator-v5-6-cb9c148b9297@kernel.org
Signed-off-by: Kairui Song <kasong@tencent.com>
Reported-by: Barry Song <21cnbao@gmail.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kairui Song 2024-07-30 23:49:18 -07:00 committed by Andrew Morton
parent 650975d2b1
commit 862590ac37
1 changed files with 109 additions and 43 deletions
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152
mm/swapfile.c
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@ -53,8 +53,15 @@
static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
unsigned char);
static void free_swap_count_continuations(struct swap_info_struct *);
static void swap_entry_range_free(struct swap_info_struct *si, swp_entry_t entry,
unsigned int nr_pages);
static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
unsigned int nr_entries);
static bool folio_swapcache_freeable(struct folio *folio);
static struct swap_cluster_info *lock_cluster_or_swap_info(
struct swap_info_struct *si, unsigned long offset);
static void unlock_cluster_or_swap_info(struct swap_info_struct *si,
struct swap_cluster_info *ci);
static DEFINE_SPINLOCK(swap_lock);
static unsigned int nr_swapfiles;
@ -129,8 +136,25 @@ static inline unsigned char swap_count(unsigned char ent)
* corresponding page
*/
#define TTRS_UNMAPPED 0x2
/* Reclaim the swap entry if swap is getting full*/
/* Reclaim the swap entry if swap is getting full */
#define TTRS_FULL 0x4
/* Reclaim directly, bypass the slot cache and don't touch device lock */
#define TTRS_DIRECT 0x8
static bool swap_is_has_cache(struct swap_info_struct *si,
unsigned long offset, int nr_pages)
{
unsigned char *map = si->swap_map + offset;
unsigned char *map_end = map + nr_pages;
do {
VM_BUG_ON(!(*map & SWAP_HAS_CACHE));
if (*map != SWAP_HAS_CACHE)
return false;
} while (++map < map_end);
return true;
}
/*
* returns number of pages in the folio that backs the swap entry. If positive,
@ -141,12 +165,22 @@ 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 address_space *address_space = swap_address_space(entry);
struct swap_cluster_info *ci;
struct folio *folio;
int ret = 0;
int ret, nr_pages;
bool need_reclaim;
folio = filemap_get_folio(swap_address_space(entry), swap_cache_index(entry));
folio = filemap_get_folio(address_space, swap_cache_index(entry));
if (IS_ERR(folio))
return 0;
/* offset could point to the middle of a large folio */
entry = folio->swap;
offset = swp_offset(entry);
nr_pages = folio_nr_pages(folio);
ret = -nr_pages;
/*
* 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
@ -154,14 +188,50 @@ static int __try_to_reclaim_swap(struct swap_info_struct *si,
* 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);
if (!folio_trylock(folio))
goto out;
need_reclaim = ((flags & TTRS_ANYWAY) ||
((flags & TTRS_UNMAPPED) && !folio_mapped(folio)) ||
((flags & TTRS_FULL) && mem_cgroup_swap_full(folio)));
if (!need_reclaim || !folio_swapcache_freeable(folio))
goto out_unlock;
/*
* It's safe to delete the folio from swap cache only if the folio's
* swap_map is HAS_CACHE only, which means the slots have no page table
* reference or pending writeback, and can't be allocated to others.
*/
ci = lock_cluster_or_swap_info(si, offset);
need_reclaim = swap_is_has_cache(si, offset, nr_pages);
unlock_cluster_or_swap_info(si, ci);
if (!need_reclaim)
goto out_unlock;
if (!(flags & TTRS_DIRECT)) {
/* Free through slot cache */
delete_from_swap_cache(folio);
folio_set_dirty(folio);
ret = nr_pages;
goto out_unlock;
}
ret = ret ? folio_nr_pages(folio) : -folio_nr_pages(folio);
xa_lock_irq(&address_space->i_pages);
__delete_from_swap_cache(folio, entry, NULL);
xa_unlock_irq(&address_space->i_pages);
folio_ref_sub(folio, nr_pages);
folio_set_dirty(folio);
spin_lock(&si->lock);
/* Only sinple page folio can be backed by zswap */
if (nr_pages == 1)
zswap_invalidate(entry);
swap_entry_range_free(si, entry, nr_pages);
spin_unlock(&si->lock);
ret = nr_pages;
out_unlock:
folio_unlock(folio);
out:
folio_put(folio);
return ret;
}
@ -895,7 +965,7 @@ checks:
if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
int swap_was_freed;
spin_unlock(&si->lock);
swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY | TTRS_DIRECT);
spin_lock(&si->lock);
/* entry was freed successfully, try to use this again */
if (swap_was_freed > 0)
@ -1333,9 +1403,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
unsigned long offset = swp_offset(entry);
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);
@ -1343,23 +1410,14 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
return;
ci = lock_cluster_or_swap_info(si, offset);
if (size > 1) {
map = si->swap_map + offset;
for (i = 0; i < size; i++) {
val = map[i];
VM_BUG_ON(!(val & SWAP_HAS_CACHE));
if (val == SWAP_HAS_CACHE)
free_entries++;
}
if (free_entries == size) {
unlock_cluster_or_swap_info(si, ci);
spin_lock(&si->lock);
swap_entry_range_free(si, entry, size);
spin_unlock(&si->lock);
return;
}
if (size > 1 && swap_is_has_cache(si, offset, size)) {
unlock_cluster_or_swap_info(si, ci);
spin_lock(&si->lock);
swap_entry_range_free(si, entry, size);
spin_unlock(&si->lock);
return;
}
for (i = 0; i < size; i++, entry.val++) {
for (int 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);
@ -1519,16 +1577,7 @@ static bool folio_swapped(struct folio *folio)
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)
static bool folio_swapcache_freeable(struct folio *folio)
{
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
@ -1536,8 +1585,6 @@ bool folio_free_swap(struct folio *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,
@ -1557,6 +1604,25 @@ bool folio_free_swap(struct folio *folio)
if (pm_suspended_storage())
return false;
return true;
}
/**
* folio_free_swap() - Free the swap space used for this folio.
* @folio: The folio to remove.
*
* If swap is getting full, or if there are no more mappings of this folio,
* then call folio_free_swap to free its swap space.
*
* Return: true if we were able to release the swap space.
*/
bool folio_free_swap(struct folio *folio)
{
if (!folio_swapcache_freeable(folio))
return false;
if (folio_swapped(folio))
return false;
delete_from_swap_cache(folio);
folio_set_dirty(folio);
return true;
@ -1633,7 +1699,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
* to the next boundary.
*/
nr = __try_to_reclaim_swap(si, offset,
TTRS_UNMAPPED | TTRS_FULL);
TTRS_UNMAPPED | TTRS_FULL);
if (nr == 0)
nr = 1;
else if (nr < 0)