From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 59D51606A326 for ; Wed, 11 Nov 2026 01:56:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=itp0oXEf Received: by kanga.kvack.org (Postfix) id 485A56B05B9; Tue, 10 Nov 2026 20:56:15 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 40FF06B05BB; Tue, 10 Nov 2026 20:56:15 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 34ED26B05B9; Tue, 10 Nov 2026 20:56:15 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 0C8156B05B9 for ; Tue, 10 Nov 2026 20:56:15 -0500 (EST) Received: from smtpin10.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 7145340167 for ; Wed, 11 Nov 2026 01:56:14 +0000 (UTC) X-FDA: 85421173068.10.5BF2E8E Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf14.hostedemail.com (Postfix) with ESMTP id C07C4100004 for ; Wed, 11 Nov 2026 01:56:12 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=itp0oXEf; spf=pass (imf14.hostedemail.com: domain of snitzer@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=snitzer@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1794362172; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=tnDCs+7uPBjV4AWzwRSdGW/2w1/1J5xqMVOU9/AJamg=; b=byb75KtpgzmwesE2GJ+7/35HpIINDDgwiNC6XdJvHBjJVIcqCBtiA19hLmv7erZ0U2786d X6jqsfanuSGaRpM7COCh8v0dc0WlmfKQKZGy9TTkSxXPWvBUUS828FqugjnZyOM2IXZArr GoMlxQPwF3uRG1HjCLeLQS+fFnpwk9M= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794362172; b=BrnIdVHzo5U4aLK7y38Wt3t0mmbfpAlfttwvHTq24XE6UNd0GyhwugLkbToMtOcv87Rb9X MC0fqFASLTDIsdVGLlEC768h50OGBPYeIN8JaC8jN0UCY6Gu4mtH6AHeBK70HRNM1Z6GMb EYArY0qmwThDdVJOU+Dg3ruZTz/VWFc= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=itp0oXEf; spf=pass (imf14.hostedemail.com: domain of snitzer@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=snitzer@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id B2F4C47312; Wed, 11 Nov 2026 01:56:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6292C1F0089F; Wed, 11 Nov 2026 01:56:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794362171; bh=tnDCs+7uPBjV4AWzwRSdGW/2w1/1J5xqMVOU9/AJamg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=itp0oXEfchQuxyVTQgHfLH3S90MLaAoZA5X2/d0kX5lDDas4YJK5T4vozbrzLNfpz tryNN9EzJz3tpWsQvXrF9fS6ABhvRXaOtkVSMJEpZjPjBkl9nIkc3PB4gPu4oC1dWP VZKBE/2Sq2SvOBrATM26VzSwJccjHwdrPFFroKHIRhtqetdb0iEpviFLPStr+igjSj sJugrMg6zAR37DnLZl84Fr5ZoEpHw3CFNvaoy6HraT6UBLjb6aTYtimpg/X5GN4MV1 jZf199wif6A2IuLSjkZ765v6SEgidSQsnW2tuB4Kp2dhbsQNB0/8gJgO19zSyNYeyX DKQtW64TwMUCw== From: Mike Snitzer To: Matthew Wilcox , Jan Kara , linux-mm@kvack.org, Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Chuck Lever , Jeff Layton , linux-nfs@vger.kernel.org Subject: [PATCH v11 2/7] mm: take a folio off WB_DONTCACHE_DIRTY only if it was counted there Date: Tue, 10 Nov 2026 20:56:02 -0500 Message-ID: <20261111015607.46338-3-snitzer@kernel.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20261111015607.46338-1-snitzer@kernel.org> References: <20261111015607.46338-1-snitzer@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C07C4100004 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-Stat-Signature: kty4t5cr6qn1sdu3btak7b6b4has8ze5 X-Rspam-User: X-HE-Tag: 1794362172-542817 X-HE-Meta: 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 D3c13Cow FjufPo33c5uFAPhtbudU/XvNOsCQzS5Tly5e+8d3hnAEtxeaAW+IpGyYMgCg18NRcrbBzesipHRGAo617kUTnnh/56R//ovATqhEka7fNhbOldwS8d3NTfuq9paTN/NSKdThuNmBj7QWJ85tw+JvmW7BZ5Mvtmk/8afrCGs19F4RXjm2ue5iaLjdh7TT5p1AoqnMuErhWdX8QC0HsUwb6AeuQ/UYwp1K2RChGca+QCABKrHD+IlgHRcoj1eDk0tH1MEXQI0ck49WZoy5NQUKW/pHwNqsyKnsGaJrFj6RuRmNLVbKZmKn4Vcm4XA== 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