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 14113CA0FED for ; Fri, 5 Sep 2025 14:43:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 694E88E0009; Fri, 5 Sep 2025 10:43:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 645E18E0005; Fri, 5 Sep 2025 10:43:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 55B2B8E0009; Fri, 5 Sep 2025 10:43:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 4317A8E0005 for ; Fri, 5 Sep 2025 10:43:52 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 57461B76D4 for ; Fri, 5 Sep 2025 14:43:50 +0000 (UTC) X-FDA: 83855465820.05.E1A9FB2 Received: from mail-wm1-f49.google.com (mail-wm1-f49.google.com [209.85.128.49]) by imf29.hostedemail.com (Postfix) with ESMTP id 5234F120003 for ; Fri, 5 Sep 2025 14:43:48 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=JSL63xeM; spf=pass (imf29.hostedemail.com: domain of usamaarif642@gmail.com designates 209.85.128.49 as permitted sender) smtp.mailfrom=usamaarif642@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1757083428; 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=gwJaAVz81BObi+H/arsIEh5sBDwsjXLHGvxI5p+NvZc=; b=naTzI0UFKmIZl2RqQcu15n2kKYTMpnwbvZDrlr6YqhR+PKrsGgSblGrCYDmBeqUpQ0xaqL 8FArZ+k1uuk+ZKfIAuEM/IsiBPyp1LvVbueHVG/cKZddzQHMNmG5J+8JvWHMuCHFbSX2U0 /XeHn3olh171783aZ1c6EXMhVliyg90= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=JSL63xeM; spf=pass (imf29.hostedemail.com: domain of usamaarif642@gmail.com designates 209.85.128.49 as permitted sender) smtp.mailfrom=usamaarif642@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1757083428; a=rsa-sha256; cv=none; b=0tosUMqJnK9SqaemjnaGYf2KxzgXHhR3jCl7/5ESsANwdvYq+kAodIc7/prqkiLoV44WGf tjyOAuzPychLa07GvFckbboGwViZbgWnVCrd/gEf4Kh6CgcByKuvHG6609GgDGb+m5qhRM SrMsrck0U5CrrmyKlX+9VLnlbrIcpDA= Received: by mail-wm1-f49.google.com with SMTP id 5b1f17b1804b1-45ddcb1f495so1063235e9.1 for ; Fri, 05 Sep 2025 07:43:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1757083427; x=1757688227; darn=kvack.org; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=gwJaAVz81BObi+H/arsIEh5sBDwsjXLHGvxI5p+NvZc=; b=JSL63xeMLDMn66o8ef4I49U3ccDyFHU+fEgvLjKY1RC3OZXMcfx2FimW5RdZFYBFZ5 z9MZO36wCZppuSQknuG+nhcDyZVpx8JzqOwng6S2ovM1EBBx2Xu3ctwTZZfRKlhfJSVx 6DtQF4J8yOQK11Uybzf5EBzw4EOb0SXasLedmdN9mpmEvKkhjplA9F87vBXRdYB5Rqfu ivmwAgbF5ScTi6WdF38rDzTYP3bmu/r5HqK+I/mHMKrpv36M7NdsDVsHm4W7ZWHxBfxj E8yJJvYzJXqZ4ohte71KLg+dtAfitwY5W8KU6A6HG1SPIBmC3pEpGLvYasECVWD7prBk zvNw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757083427; x=1757688227; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=gwJaAVz81BObi+H/arsIEh5sBDwsjXLHGvxI5p+NvZc=; b=Z1j7kMMBhaJDtWzza8rt/1vTiusij/w+xScL2nHBJKQJdIMCmAZnPdzB/yIaWt5jdp v0sOI/hAHpuAEETjqF8p+qY2NU+WfjXimHhkHM5SDL7TdbypyA3GW0qUQUXFRqjzFWwj Wj5URmdz2pUt/J2o6v239xtFmCHa0DdXeOvhjqr75NmGooRC97A01U329ItOtmZ3lqwi btxczV5Yvh0rDtaIcn28JxKPsHBBD3zdGQgogWU1KZUCmYJaNVZr5Pz7KYED9MKZ+B+j bxnqnV52a0s+oOgKenRBCGtPa1epA8STM+5mJCQovstN4F2ly0SIYGJvMX3siAgyJ8p/ BFog== X-Forwarded-Encrypted: i=1; AJvYcCUAX6+XU+vcpXb90Kr8oc98q86vyzFv5/pZxWCHVpcPTMLg3m4amY+lD37KyCy1TrzhXvVauyEByg==@kvack.org X-Gm-Message-State: AOJu0YxKSVuYgLap/o0jilYv5VLcYD5WCV03apo684LfL7VQkeVqHA0g Y0ZnR+DfE/RYapQYPa1b4vluq7IBjS157kU1jRhJ96hpVb5ARR5ic9r7 X-Gm-Gg: ASbGncs+4axmufpgXhkgauO4SuTK0THj0PNs1B9tXCDO3sUWmzY3sp/lezdHaMMjHrB WrM9S5V74aYmGKj2DmRXBvwpv/Q9QZsuHGEjgiP05SykOSGhkAUA6OyiBrzKPo6hJZvd3tspmHX E9F6r6kwggs4MMWEwOd8OCRvY6WikPMbiO1JnSNNal3VWyeZq3ow3Q+O9Z0A7Av1EN69FuE+Scs sSbR3l5zaWZi8LRWjgFPB0rGNZEaj8Gsyw0pIZv4TMgKsKdvsOB2LDgFTRkGkQvoSxzzjthTOB7 gFRS+PCwcewT47NbT8EV8JGNKwBXfm3lw0nycP2xE3C5xbePS75P2Eb8Z2G/qgZ2HSw4o4kUUrB Mum7D4NcPmi9IBAjEEhdqjSX0a3sN00rkLZKMadIDhSzmkV1D3+l3RJqAqkfoFQ4G+7Lhdww= X-Google-Smtp-Source: AGHT+IGTEmyI3GJ5+Bu7s94GgTAOG29U9ayxB6BDUIhPl8/Z0BjlcNHrWbUoE21RMRPW1bmYwLPBlg== X-Received: by 2002:a05:600c:4715:b0:45b:43cc:e558 with SMTP id 5b1f17b1804b1-45b8558ad00mr208282635e9.35.1757083426547; Fri, 05 Sep 2025 07:43:46 -0700 (PDT) Received: from ?IPV6:2a03:83e0:1126:4:1449:d619:96c0:8e08? ([2620:10d:c092:500::4:4f66]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b8f2d3c88sm200044495e9.19.2025.09.05.07.43.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 Sep 2025 07:43:45 -0700 (PDT) Message-ID: Date: Fri, 5 Sep 2025 15:43:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/huge_memory: fix shrinking of all-zero THPs with max_ptes_none default Content-Language: en-GB To: Zi Yan , David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song References: <20250905141137.3529867-1-david@redhat.com> <7B0B1E09-5083-449F-851D-FD63D32D2B3D@nvidia.com> From: Usama Arif In-Reply-To: <7B0B1E09-5083-449F-851D-FD63D32D2B3D@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5234F120003 X-Stat-Signature: cs6g8gipckqjw6qxgxxwx1ers73wbmic X-Rspam-User: X-HE-Tag: 1757083428-408237 X-HE-Meta: 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 PpYJBRJN 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 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 05/09/2025 15:37, Zi Yan wrote: > On 5 Sep 2025, at 10:11, David Hildenbrand wrote: > >> We added an early exit in thp_underused(), probably to avoid scanning >> pages when there is no chance for success. >> >> However, assume we have max_ptes_none = 511 (default). >> >> Nothing should stop us from freeing all pages part of a THP that >> is completely zero (512) and khugepaged will for sure not try to >> instantiate a THP in that case (512 shared zeropages). >> >> This can just trivially happen if someone writes a single 0 byte into a >> PMD area, or of course, when data ends up being zero later. >> >> So let's remove that early exit. >> >> Do we want to CC stable? Hm, not sure. Probably not urgent. >> >> Note that, as default, the THP shrinker is active >> (/sys/kernel/mm/transparent_hugepage/shrink_underused = 1), and all >> THPs are added to the deferred split lists. However, with the >> max_ptes_none default we would never scan them. We would not do that. If >> that's not desirable, we should just disable the shrinker as default, >> also not adding all THPs to the deferred split lists. >> >> Easy to reproduce: >> >> 1) Allocate some THPs filled with 0s >> >> >> #include >> #include >> #include >> #include >> #include >> >> const size_t size = 1024*1024*1024; >> >> int main(void) >> { >> size_t offs; >> char *area; >> >> area = mmap(0, size, PROT_READ | PROT_WRITE, >> MAP_ANON | MAP_PRIVATE, -1, 0); >> if (area == MAP_FAILED) { >> printf("mmap failed\n"); >> exit(-1); >> } >> madvise(area, size, MADV_HUGEPAGE); >> >> for (offs = 0; offs < size; offs += getpagesize()) >> area[offs] = 0; >> pause(); >> } >> <\prog.c> >> >> 2) Trigger the shrinker >> >> E.g., memory pressure through memhog >> >> 3) Observe that THPs are not getting reclaimed >> >> $ cat /proc/`pgrep prog`/smaps_rollup >> >> Would list ~1GiB of AnonHugePages. With this fix, they would get >> reclaimed as expected. >> >> Fixes: dafff3f4c850 ("mm: split underused THPs") >> Cc: Andrew Morton >> Cc: Lorenzo Stoakes >> Cc: Zi Yan >> Cc: Baolin Wang >> Cc: "Liam R. Howlett" >> Cc: Nico Pache >> Cc: Ryan Roberts >> Cc: Dev Jain >> Cc: Barry Song >> Cc: Usama Arif >> Signed-off-by: David Hildenbrand >> --- >> mm/huge_memory.c | 3 --- >> 1 file changed, 3 deletions(-) >> > LGTM. Acked-by: Zi Yan > > I also notice that thp_underused() checks num_zero_pages directly > against khugepaged_max_ptes_none. This means mTHPs will never be regarded > as underused. A similar issue you are discussing in Nico’s khugepaged > mTHP support. Maybe checks against these khugepaged_max* variables > should be calculated based on nr_pages of a large folio, like > making these variables a ratio in other discussion. I unfortunately didnt follow the series in the latest revisions. In the earlier revisions, I think it was decided to not add mTHPs to shrinker as a start, as there are diminshing returns for smaller THPs and having a lot of smaller mTHPs in the deferred list might mean that we get to PMD mapped THPs a lot slower? > > Best Regards, > Yan, Zi