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Sun, 16 Nov 2025 10:12:41 -0800 (PST) From: Kairui Song Date: Mon, 17 Nov 2025 02:11:48 +0800 Subject: [PATCH v2 07/19] mm/shmem: never bypass the swap cache for SWP_SYNCHRONOUS_IO Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251117-swap-table-p2-v2-7-37730e6ea6d5@tencent.com> References: <20251117-swap-table-p2-v2-0-37730e6ea6d5@tencent.com> In-Reply-To: <20251117-swap-table-p2-v2-0-37730e6ea6d5@tencent.com> To: linux-mm@kvack.org Cc: Andrew Morton , Baoquan He , Barry Song , Chris Li , Nhat Pham , Yosry Ahmed , David Hildenbrand , Johannes Weiner , Youngjun Park , Hugh Dickins , Baolin Wang , Ying Huang , Kemeng Shi , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , linux-kernel@vger.kernel.org, Kairui Song X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1763316712; l=7744; i=kasong@tencent.com; s=kasong-sign-tencent; h=from:subject:message-id; bh=VBm+UEMLrddKYoSogqdhFKlPao5i04J0iZkpSQUK7s8=; b=OMyWgLnxFZhhYXCBMOq7x6j0wLOxEOMfr4tgzF4mbDOUpePSfD6onGeAcusToycPpmW0tCFjg QnL39dn0BkTAzqNhPuujC2gwQcnuilJGoYGW2z3jlHfTckMXIjBbKiA X-Developer-Key: i=kasong@tencent.com; a=ed25519; pk=kCdoBuwrYph+KrkJnrr7Sm1pwwhGDdZKcKrqiK8Y1mI= From: Kairui Song Now the overhead of the swap cache is trivial to none, bypassing the swap cache is no longer a valid optimization. We have removed the cache bypass swapin for anon memory, now do the same for shmem. Many helpers and functions can be dropped now. Signed-off-by: Kairui Song --- mm/shmem.c | 65 +++++++++++++++++------------------------------------------ mm/swap.h | 4 ---- mm/swapfile.c | 35 +++++++++----------------------- 3 files changed, 27 insertions(+), 77 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index fc835b3e4914..8b711b8bcdba 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2001,10 +2001,9 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode, swp_entry_t entry, int order, gfp_t gfp) { struct shmem_inode_info *info = SHMEM_I(inode); + struct folio *new, *swapcache; int nr_pages = 1 << order; - struct folio *new; gfp_t alloc_gfp; - void *shadow; /* * We have arrived here because our zones are constrained, so don't @@ -2044,34 +2043,19 @@ static struct folio *shmem_swap_alloc_folio(struct inode *inode, goto fallback; } - /* - * Prevent parallel swapin from proceeding with the swap cache flag. - * - * Of course there is another possible concurrent scenario as well, - * that is to say, the swap cache flag of a large folio has already - * been set by swapcache_prepare(), while another thread may have - * already split the large swap entry stored in the shmem mapping. - * In this case, shmem_add_to_page_cache() will help identify the - * concurrent swapin and return -EEXIST. - */ - if (swapcache_prepare(entry, nr_pages)) { + swapcache = swapin_folio(entry, new); + if (swapcache != new) { folio_put(new); - new = ERR_PTR(-EEXIST); - /* Try smaller folio to avoid cache conflict */ - goto fallback; + if (!swapcache) { + /* + * The new folio is charged already, swapin can + * only fail due to another raced swapin. + */ + new = ERR_PTR(-EEXIST); + goto fallback; + } } - - __folio_set_locked(new); - __folio_set_swapbacked(new); - new->swap = entry; - - memcg1_swapin(entry, nr_pages); - shadow = swap_cache_get_shadow(entry); - if (shadow) - workingset_refault(new, shadow); - folio_add_lru(new); - swap_read_folio(new, NULL); - return new; + return swapcache; fallback: /* Order 0 swapin failed, nothing to fallback to, abort */ if (!order) @@ -2161,8 +2145,7 @@ static int shmem_replace_folio(struct folio **foliop, gfp_t gfp, } static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index, - struct folio *folio, swp_entry_t swap, - bool skip_swapcache) + struct folio *folio, swp_entry_t swap) { struct address_space *mapping = inode->i_mapping; swp_entry_t swapin_error; @@ -2178,8 +2161,7 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index, nr_pages = folio_nr_pages(folio); folio_wait_writeback(folio); - if (!skip_swapcache) - swap_cache_del_folio(folio); + swap_cache_del_folio(folio); /* * Don't treat swapin error folio as alloced. Otherwise inode->i_blocks * won't be 0 when inode is released and thus trigger WARN_ON(i_blocks) @@ -2279,7 +2261,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, softleaf_t index_entry; struct swap_info_struct *si; struct folio *folio = NULL; - bool skip_swapcache = false; int error, nr_pages, order; pgoff_t offset; @@ -2322,7 +2303,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, folio = NULL; goto failed; } - skip_swapcache = true; } else { /* Cached swapin only supports order 0 folio */ folio = shmem_swapin_cluster(swap, gfp, info, index); @@ -2378,9 +2358,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, * and swap cache folios are never partially freed. */ folio_lock(folio); - if ((!skip_swapcache && !folio_test_swapcache(folio)) || - shmem_confirm_swap(mapping, index, swap) < 0 || - folio->swap.val != swap.val) { + if (!folio_matches_swap_entry(folio, swap) || + shmem_confirm_swap(mapping, index, swap) < 0) { error = -EEXIST; goto unlock; } @@ -2412,12 +2391,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, if (sgp == SGP_WRITE) folio_mark_accessed(folio); - if (skip_swapcache) { - folio->swap.val = 0; - swapcache_clear(si, swap, nr_pages); - } else { - swap_cache_del_folio(folio); - } + swap_cache_del_folio(folio); folio_mark_dirty(folio); swap_free_nr(swap, nr_pages); put_swap_device(si); @@ -2428,14 +2402,11 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, if (shmem_confirm_swap(mapping, index, swap) < 0) error = -EEXIST; if (error == -EIO) - shmem_set_folio_swapin_error(inode, index, folio, swap, - skip_swapcache); + shmem_set_folio_swapin_error(inode, index, folio, swap); unlock: if (folio) folio_unlock(folio); failed_nolock: - if (skip_swapcache) - swapcache_clear(si, folio->swap, folio_nr_pages(folio)); if (folio) folio_put(folio); put_swap_device(si); diff --git a/mm/swap.h b/mm/swap.h index 214e7d041030..e0f05babe13a 100644 --- a/mm/swap.h +++ b/mm/swap.h @@ -403,10 +403,6 @@ static inline int swap_writeout(struct folio *folio, return 0; } -static inline void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr) -{ -} - static inline struct folio *swap_cache_get_folio(swp_entry_t entry) { return NULL; diff --git a/mm/swapfile.c b/mm/swapfile.c index a2bb09867f1e..a433445e9225 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1613,22 +1613,6 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry) return NULL; } -static void swap_entries_put_cache(struct swap_info_struct *si, - swp_entry_t entry, int nr) -{ - unsigned long offset = swp_offset(entry); - struct swap_cluster_info *ci; - - ci = swap_cluster_lock(si, offset); - if (swap_only_has_cache(si, offset, nr)) { - swap_entries_free(si, ci, entry, nr); - } else { - for (int i = 0; i < nr; i++, entry.val++) - swap_entry_put_locked(si, ci, entry, SWAP_HAS_CACHE); - } - swap_cluster_unlock(ci); -} - static bool swap_entries_put_map(struct swap_info_struct *si, swp_entry_t entry, int nr) { @@ -1764,13 +1748,21 @@ void swap_free_nr(swp_entry_t entry, int nr_pages) void put_swap_folio(struct folio *folio, swp_entry_t entry) { struct swap_info_struct *si; + struct swap_cluster_info *ci; + unsigned long offset = swp_offset(entry); int size = 1 << swap_entry_order(folio_order(folio)); si = _swap_info_get(entry); if (!si) return; - swap_entries_put_cache(si, entry, size); + ci = swap_cluster_lock(si, offset); + if (swap_only_has_cache(si, offset, size)) + swap_entries_free(si, ci, entry, size); + else + for (int i = 0; i < size; i++, entry.val++) + swap_entry_put_locked(si, ci, entry, SWAP_HAS_CACHE); + swap_cluster_unlock(ci); } int __swap_count(swp_entry_t entry) @@ -3784,15 +3776,6 @@ int swapcache_prepare(swp_entry_t entry, int nr) return __swap_duplicate(entry, SWAP_HAS_CACHE, nr); } -/* - * Caller should ensure entries belong to the same folio so - * the entries won't span cross cluster boundary. - */ -void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr) -{ - swap_entries_put_cache(si, entry, nr); -} - /* * 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 -- 2.51.2