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bh=tnDCs+7uPBjV4AWzwRSdGW/2w1/1J5xqMVOU9/AJamg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bRB/Zcj5tBHqofQ1FhMUoIae7WIVhuFumByqTXTwNMROaKdkdEhhKzAuo3L+PSEWA jsmvOP0LuwA7NC8AL+y1lWWToofAEXl93LpuN75PVTgKPV0WvznroS38D72xnXOnbX +fbeYmyTbMfQsXaKotTl/AuXa9s/f7GKkoexAcW3GSEotWqMizZhL0w1w8wQq7KDO6 qgN4rCP16V3UPJuz06vZOKsPFl/ik1T/wHkd6XdoRqJ0V0ujf6qYEmO2ukYrYkP17k 5/2grxcRwprHDzvjJ2sykwsEZZz9voqXZp7xNxwQiHimSRA/Tgla+WWWzB2/4pHdeS MHztBApi+OluQ== From: Mike Snitzer To: Matthew Wilcox , Jan Kara , linux-mm@kvack.org, Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Mike Snitzer , Chuck Lever , Jeff Layton , linux-nfs@vger.kernel.org Subject: [PATCH v12 2/7] mm: take a folio off WB_DONTCACHE_DIRTY only if it was counted there Date: Thu, 12 Nov 2026 14:09:05 -0500 Message-ID: <20261112190911.84702-3-snitzer@kernel.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20261112190911.84702-1-snitzer@kernel.org> References: <20261112190911.84702-1-snitzer@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 939A84000B X-Stat-Signature: sxjysfbif3gzjfjbsiefkfyijoz4bwi7 X-Rspam-User: X-HE-Tag: 1794510559-56926 X-HE-Meta: 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 rxvp7GAg yodX7Qgdj4P2esd5tkXvrKIS5j7RPMSF8p24imz9wCmhcgGHII+j9fL1aUo3V8HPtC+tMaDAgf26ZvrhnO/yJM67qexUy9UnghVskvp0emSm39WuuXzUsMvFFLlTGdOjgXvlhijp++NIkcxqx3pcGzA8TyeQEKvhlIhDiKPJGjGICSGCrX9cokowBoOAWnE9HVXl1/zyk3Iz+Yh3HyFlDbH6eMhsB2nkSDEZIoyo8+cmxcUHEC+SmAAbfrwZTO4cr0+fl7kiC/ONIWdrotbr+jW/JvuFPw50kJQO52bKJ96R2c0v5G6sZTeseZA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 A cached lookup that finds a dropbehind folio clears the flag and subtracts the folio from WB_DONTCACHE_DIRTY if PG_dirty is set. That test races with the dirtying of the folio. filemap_dirty_folio() sets PG_dirty before folio_account_dirtied() counts the folio, so a lookup in between subtracts a folio that was never added. The lookup also does not hold the folio lock. Every other path that subtracts a dirty folio from the counter holds it, so the lookup can subtract the folio a second time. Either way the counter drifts, and once it is negative the DONTCACHE writeback kick writes nothing. Fix this by having filemap_clear_dropbehind() clear the dropbehind flag of a folio that a cached lookup found, and take the folio off WB_DONTCACHE_DIRTY if it is counted there. With the folio locked and the i_pages lock held, the folio is counted if both PG_dirty and the dirty tag are set. A folio that another task has locked keeps the flag. Fixes: 88d6f128d06d ("mm: track DONTCACHE dirty pages per bdi_writeback") Reviewed-by: Jeff Layton Signed-off-by: Mike Snitzer --- mm/filemap.c | 42 ++++++++++++++++++++++++++++-------------- 1 file changed, 28 insertions(+), 14 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 437113addbddf..98ce955404127 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1956,22 +1956,36 @@ void *filemap_get_entry(struct address_space *mapping, pgoff_t index) return folio; } -/* Clear the dropbehind flag of a folio that a cached lookup found. */ +/* + * Clear the dropbehind flag of a folio that a cached lookup found, and take + * the folio off WB_DONTCACHE_DIRTY if it is counted there. With the folio + * locked and the i_pages lock held, the folio is counted if both PG_dirty and + * the dirty tag are set. A folio that another task has locked keeps the flag. + */ static void filemap_clear_dropbehind(struct address_space *mapping, - struct folio *folio) + struct folio *folio, bool locked) { - if (!folio_test_clear_dropbehind(folio)) - return; - if (folio_test_dirty(folio) && mapping_can_writeback(mapping)) { - struct inode *inode = mapping->host; - struct bdi_writeback *wb; - struct wb_lock_cookie cookie = {}; - long nr = folio_nr_pages(folio); + unsigned long flags; - wb = unlocked_inode_to_wb_begin(inode, &cookie); - wb_stat_mod(wb, WB_DONTCACHE_DIRTY, -nr); - unlocked_inode_to_wb_end(inode, &cookie); + if (!locked) { + if (!folio_trylock(folio)) + return; + if (unlikely(folio->mapping != mapping)) + goto out; } + if (!mapping_can_writeback(mapping)) { + folio_clear_dropbehind(folio); + goto out; + } + xa_lock_irqsave(&mapping->i_pages, flags); + if (folio_test_clear_dropbehind(folio) && folio_test_dirty(folio) && + xa_get_mark(&mapping->i_pages, folio->index, PAGECACHE_TAG_DIRTY)) + wb_stat_mod(inode_to_wb(mapping->host), WB_DONTCACHE_DIRTY, + -folio_nr_pages(folio)); + xa_unlock_irqrestore(&mapping->i_pages, flags); +out: + if (!locked) + folio_unlock(folio); } /** @@ -2105,8 +2119,8 @@ struct folio *__filemap_get_folio_mpol(struct address_space *mapping, if (!folio) return ERR_PTR(-ENOENT); /* not an uncached lookup, clear uncached if set */ - if (!(fgp_flags & FGP_DONTCACHE)) - filemap_clear_dropbehind(mapping, folio); + if (!(fgp_flags & FGP_DONTCACHE) && folio_test_dropbehind(folio)) + filemap_clear_dropbehind(mapping, folio, fgp_flags & FGP_LOCK); return folio; } EXPORT_SYMBOL(__filemap_get_folio_mpol); -- 2.52.0