From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B2404E73146 for ; Mon, 2 Feb 2026 08:55:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 25FB86B008C; Mon, 2 Feb 2026 03:55:40 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 22A016B0092; Mon, 2 Feb 2026 03:55:40 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 135AB6B0093; Mon, 2 Feb 2026 03:55:40 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 0262C6B008C for ; Mon, 2 Feb 2026 03:55:39 -0500 (EST) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id B57B51604F0 for ; Mon, 2 Feb 2026 08:55:39 +0000 (UTC) X-FDA: 84398908398.20.5239833 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf05.hostedemail.com (Postfix) with ESMTP id E03C1100003 for ; Mon, 2 Feb 2026 08:55:37 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=qj4t1a7p; spf=pass (imf05.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@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=1770022538; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wXy0RfaqOoDKiVan2YzXLhJ3luqHhsG4xawRw1SGW5A=; b=1aZPZrR4OHQCLIbQQ7p2GR8+nWiL+KM+ycCnuIzUDn0MlTqM81pklLDgfhRb4lxCDrTn8J XhAD+V4oxpHGoeGvKqX8OoRU9KNec4AawITabOQ3x61sapnNz/u/USiJ4kddd4YFwvJbLo 8Fxgh1xXHSY3UiMDrcvIxXFxZPTxfno= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=qj4t1a7p; spf=pass (imf05.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1770022538; a=rsa-sha256; cv=none; b=c+a6ghLup+i6gUh7eRlppqVS/AsH/o+o4Uze+L405FaBtmL1pryuDb84vhymSJKVY5Mzzj /2pI8SOzCxgr2qb3WvkfShkqKhNh3XH1CMdMal9nNr4Taf4pCVctQlIVi3EaHEn4x1B3Fk RpxevzFXMN1L80LlsvehhS0Ny3dAIFI= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id C2966442B5; Mon, 2 Feb 2026 08:55:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0F611C116C6; Mon, 2 Feb 2026 08:55:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770022536; bh=BDzkEXTSn4OsyMImxJsTqnJmwvMEHbv2lChkyPpJg2U=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=qj4t1a7p41f5H39L2b4xDJNgIgNDKQHW0XEb1YYzmWWL6Bx3POHiVAaLh0VnLIhY/ 6QXOQo5d7NsaJ1qW2UW0NS+n8+clnWz7Oe0jfjFWT297upD7mB0F4nuPOeDAYJ7k1r R8vF6RnWBNr0T314Ow+Kk6ZHWmPxFpltzGwZhl44s2ACnsxMQ+2ykoKEunETDBgGge VoI52D2RtMqu17s6fIkZKLrCuPJlsJnGw4XiyC9WGJyqTKexrvhEkr3CsxOkhrEwU4 FTwCbTIPOLMHk+xGMwJzUFIMGZMdk2iSpIVWyZauTTL9GoCvcMyd59CJsY9nN7eGol 0HG9TSYTjo9Mw== Message-ID: <3edb394e-ecc4-4bee-973c-a801aa6e7282@kernel.org> Date: Mon, 2 Feb 2026 09:55:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: khugepaged: fix NR_FILE_PAGES and NR_SHMEM in collapse_file() From: "David Hildenbrand (arm)" To: Shakeel Butt , Andrew Morton Cc: Johannes Weiner , Rik van Riel , Song Liu , Kiryl Shutsemau , Usama Arif , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Matthew Wilcox , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260130042925.2797946-1-shakeel.butt@linux.dev> <10e483b2-2aa2-48a9-bc96-2cfb8125824d@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAa2VybmVsLm9yZz7CwY0EEwEIADcWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaKYhwAIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA/4Naa5EP/3a1 9sgS9m7oiR0uenlj+C6kkIKlpWKRfGH/WvtFaHr/y06TKnWn6cMOZzJQ+8S39GOteyCCGADh 6ceBx1KPf6/AvMktnGETDTqZ0N9roR4/aEPSMt8kHu/GKR3gtPwzfosX2NgqXNmA7ErU4puf zica1DAmTvx44LOYjvBV24JQG99bZ5Bm2gTDjGXV15/X159CpS6Tc2e3KvYfnfRvezD+alhF XIym8OvvGMeo97BCHpX88pHVIfBg2g2JogR6f0PAJtHGYz6M/9YMxyUShJfo0Df1SOMAbU1Q Op0Ij4PlFCC64rovjH38ly0xfRZH37DZs6kP0jOj4QdExdaXcTILKJFIB3wWXWsqLbtJVgjR YhOrPokd6mDA3gAque7481KkpKM4JraOEELg8pF6eRb3KcAwPRekvf/nYVIbOVyT9lXD5mJn IZUY0LwZsFN0YhGhQJ8xronZy0A59faGBMuVnVb3oy2S0fO1y/r53IeUDTF1wCYF+fM5zo14 5L8mE1GsDJ7FNLj5eSDu/qdZIKqzfY0/l0SAUAAt5yYYejKuii4kfTyLDF/j4LyYZD1QzxLC MjQl36IEcmDTMznLf0/JvCHlxTYZsF0OjWWj1ATRMk41/Q+PX07XQlRCRcE13a8neEz3F6we 08oWh2DnC4AXKbP+kuD9ZP6+5+x1H1zEzsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCgh Cj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseB fDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts 6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiu Qmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKB Tccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvF FFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh 2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRk F3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0L LH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4v q7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmic2qsF CSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvVQ0x8xXvoGJwZ rk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q/y06TrTb1n4n 7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPFQKzhRRktBMK4 GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLoPn9kgHD3hRBa Yakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX63T6oO2Libzz 7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt2slI4VcPNnz+ vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMBgoisDB8ceYxO cFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY2x3snF8q7U9G EIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqBgzK8ePtDTqRM qZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8fa0= In-Reply-To: <10e483b2-2aa2-48a9-bc96-2cfb8125824d@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E03C1100003 X-Stat-Signature: z5u6sebu4yowib53dfh4b886rouf59gm X-Rspam-User: X-HE-Tag: 1770022537-751203 X-HE-Meta: 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 Qd6Cq9Xr cQ09Fsm0g69cc/0+uFt2s7CjxDEtFEXLMEpmpudROgauMdYm9pT4V7tYkO4YMQdcAQm4dFWmL4GjaqkUM1HLUi0ecgr7gh4UVSVPivhxqrksoiwjFVVxYJjSicFhM5Cm0Im664zJ+TDIrzYDOzFCJkf6qyEhFvL+G0NYknnsFvhyyaEsupz/3npCx2HkyZDUh1SKgjfxOY4XJ6ovE1SoBgTOLFQ+T8OuaHDYdRUatHz6h0Ijlvvln2A/6MouclEgUYlujk60RhuXSXpSLuuToWyzetVmGhw9Di3Q8g/swn5cweHCcq1dikT957YqaKhlR5v2EnlmXJ7prJrg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/2/26 09:54, David Hildenbrand (arm) wrote: > On 1/30/26 05:29, Shakeel Butt wrote: >> In META's fleet, we observed high-level cgroups showing zero file memcg >> stats while their descendants had non-zero values. Investigation using >> drgn revealed that these parent cgroups actually had negative file stats, >> aggregated from their children. >> >> This issue became more frequent after deploying thp-always more widely, >> pointing to a correlation with THP file collapsing. The root cause is >> that collapse_file() assumes old folios and the new THP belong to the >> same node and memcg. When this assumption breaks, stats become skewed. >> The bug affects not just memcg stats but also per-numa stats, and not >> just NR_FILE_PAGES but also NR_SHMEM. >> >> The assumption breaks in scenarios such as: >> >> 1. Small folios allocated on one node while the THP gets allocated on a >> different node. >> >> 2. A package downloader running in one cgroup populates the page cache, >> while a job in a different cgroup executes the downloaded binary. >> >> 3. A file shared between processes in different cgroups, where one >> process faults in the pages and khugepaged (or madvise(COLLAPSE)) >> collapses them on behalf of the other. >> >> Fix the accounting by explicitly incrementing stats for the new THP and >> decrementing stats for the old folios being replaced. >> >> Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages") >> Signed-off-by: Shakeel Butt >> --- > > Acked-by: David Hildenbrand (Red Hat) Heh, forgot to adjust the shortcut Acked-by: David Hildenbrand (arm) -- Cheers David