From: Kairui Song kasong@tencent.com
mainline inclusion from mainline-v6.12-rc1 commit 862590ac3708e1cbbfb02a8ed78587b86ecba4ba category: performance bugzilla: https://gitee.com/openeuler/kernel/issues/IBC5I1
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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.o... 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 Conflicts: mm/swapfile.c Signed-off-by: Liu Shixin liushixin2@huawei.com --- mm/swapfile.c | 152 ++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 109 insertions(+), 43 deletions(-)
diff --git a/mm/swapfile.c b/mm/swapfile.c index 44726e0b8f8f..e58457b801fb 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -52,8 +52,15 @@ 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; @@ -128,8 +135,25 @@ 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, @@ -140,12 +164,22 @@ 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), offset); + folio = filemap_get_folio(address_space, offset); 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 @@ -153,14 +187,50 @@ 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; } @@ -888,7 +958,7 @@ static int scan_swap_map_slots(struct swap_info_struct *si, 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) @@ -1415,9 +1485,6 @@ 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); @@ -1425,23 +1492,14 @@ 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); @@ -1601,16 +1659,7 @@ 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);
@@ -1618,8 +1667,6 @@ 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, @@ -1639,6 +1686,25 @@ 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; @@ -1715,7 +1781,7 @@ 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)