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 07429CAC5B8 for ; Tue, 30 Sep 2025 07:36:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 662018E000B; Tue, 30 Sep 2025 03:36:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 612B88E0002; Tue, 30 Sep 2025 03:36:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 54FBA8E000B; Tue, 30 Sep 2025 03:36:47 -0400 (EDT) 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 4368B8E0002 for ; Tue, 30 Sep 2025 03:36:47 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id DA38E1405E5 for ; Tue, 30 Sep 2025 07:36:46 +0000 (UTC) X-FDA: 83945109612.17.9D8A74E Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) by imf26.hostedemail.com (Postfix) with ESMTP id 0E0B614000D for ; Tue, 30 Sep 2025 07:36:44 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=I7LfKX44; spf=pass (imf26.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1759217805; 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=nMbO9Tlys5llPIB/GKS5R/+Lw3U9d4/u9TV/lNk2GF8=; b=qRx5pj5GKBXUvUXcd9saSjGLeQop+G20B2Wk+AugODHbyG+sE6ftyvM/nViuDVMSmmIZGz F27R5N8EfeDqC79Up4PhHIRN60IvaJXihj/8WRSBT4C/8+2Fy+AkNOq5l1RB3L+Jo+CneF LQSUwo7YXoWlIIK2F38e6WnqIQrNJ4g= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1759217805; a=rsa-sha256; cv=none; b=1LZdy7gHEPMe/oqTdXvkkAVjXHtVrGI5FNv434jp1Kr4Mdo9gDjtjlND4xNq5KzxceHkYh 7VLPuzuNeOMjeYhjLmTEqZ+Jf+GMLrnOjuHGM5zMopnWb+OzTi0arXv0MUVLQJBBkdiDba BJFFoUgaI/VJ6TCD+OisOOOBM7+HvHU= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=I7LfKX44; spf=pass (imf26.hostedemail.com: domain of lance.yang@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev Message-ID: <556e072d-6bec-421a-a78c-fcde61af67f9@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1759217803; h=from:from: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; bh=nMbO9Tlys5llPIB/GKS5R/+Lw3U9d4/u9TV/lNk2GF8=; b=I7LfKX44os0xFnVKDz31DNnBjFvIrbnjN2gggYFuKyx1SoGR9d/Xs/QWF4i1I8nA2V5RWl W85GgcOtwqUi+YQglSgCu2t2Q0M0gzq8vFreEoFROs6WgbEcu960J7PO4AXZWGr9y45Q5H DN77mofyd0GxSn0DtEEpDiyjEUy/2X4= Date: Tue, 30 Sep 2025 15:36:36 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 1/1] mm/ksm: fix spurious soft-dirty bit on zero-filled page merging Content-Language: en-US To: David Hildenbrand Cc: xu.xin16@zte.com.cn, chengming.zhou@linux.dev, ran.xiaokai@zte.com.cn, yang.yang29@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ioworker0@gmail.com, akpm@linux-foundation.org References: <20250928045207.78546-1-lance.yang@linux.dev> <8476e9be-3f80-4d7a-9a38-f910661e61c6@linux.dev> <02c8cf41-116d-46ab-9d40-803cc26dbbf8@redhat.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <02c8cf41-116d-46ab-9d40-803cc26dbbf8@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 0E0B614000D X-Stat-Signature: gdsizp7ck4fzfjyjx1h5gq9useabyfpy X-Rspam-User: X-HE-Tag: 1759217804-676305 X-HE-Meta: U2FsdGVkX19cb90pjdgQc87pfXLs5XP/awizk2W+Byr1smPOaWHd+o0f3cBhLoYjJK16IpKCGtj5KR0RAhhF9ypVOt+ww30/aPf6b3VQo7eLY9OaEtXxJ1TrfpkZhBLDoSHMG1pKOOTpnsUVyhhuf6yN4WE2mg6XxON1GjU3ZVixpHDOXsWiQubQ9K29X4m84JlR4mYRGkHP0ehK6d0AbjzB+Cv1n43iFzBS5i+/56i+GjbLxl5q3NFhfMRi5BjwnYR7nNeq5P/kMzLF4zPAPcHl3YtxW46sVmUwNEaYXVtd5cS4E7TmxkhsrPpiZmV2G1yrMXbRz3MzjpW+D+WhKttSw0UEkulLeyDsa+SRFiHZteWTyMkzcH/4P6GVimPQhs0uRF8eaqUBDfbE3pz1ugWdDs1HucMZzJnbFrM18j5eW5OUDMu8fVMv586U1Np2ifazknNJ8p51sGFZdLDjY/Ni8BmoPJWUBFo9gNhxOpxD6i0Mv8sEQqCXdV/Zbpng5tx5uSCBoJacxSl/qSOZbbieWtxu8bndhch3F6spEi4jaNXXq1ukHuZ9exA/fFzPLjV0QHbTpQVX44GT6yAXxWiXAttxO6XkHEzfH0hTLASdEAwnmd0fAuLM4jklum5ByuKW17dtVQAGyumKvKaEdcxle8eGc7QZGdr96TatBecl/TiaEh1mmyOc86IE9Dkwo7t42RtWfk/7/yWEQsUxUyaoyZLyXbDt/wdRLhaBebdnp6j6JUy9J2LS+gH6mS2+uRFLQOksebCf9W83o9ltP7yDGgIxCVSrh2hDBhZNiLzEHWVLx9idL/Pvj+myWgIYpwCGYMq4zigHr1CR9leyr3J8PYCTZZlR2Ee1UW9iSGJzN0/Vs1MNZW+UO6gI2nbXBA9vjtw0aR9vEmXUDi/pNRGasYq0DepoheWzska19AvhZnoQEMTIWvNvJZT7eBwj3VZPU/f1OTUZ9gtM9a7 v+qqLLg0 qPruVKmYsgP7peYzxMf9yAfqbb/jT+ZNCe++oR4vutREOIS4L8tJ0SlS8kaEhDHXWdKSgiBTc03gel8W1UUMpvHWXSU4KekY9IDmFiMzigaaUknc0WJn+RbazIapAIMi3jQfx0HfxJ60KGo0h4VGnnnLgOJJ/DqdQX6ivc8k6rkeND8obpGjOPYWGi5E3tvHER/x6 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 2025/9/30 15:32, David Hildenbrand wrote: > On 29.09.25 12:08, Lance Yang wrote: >> >> >> On 2025/9/29 16:25, David Hildenbrand wrote: >>> On 28.09.25 06:52, Lance Yang wrote: >>>> From: Lance Yang >>>> >>>> When KSM merges a zero-filled page with the shared zeropage, it uses >>>> pte_mkdirty() to mark the new PTE for internal accounting. However, >>>> pte_mkdirty() unconditionally sets both the hardware dirty bit and the >>>> soft-dirty bit. >>>> >>> >>> Right, that's one think we should clean up at one point. >> >> Got it. I’ll take a look when I get a chance ;) >> >>> >>>> This behavior causes false positives in userspace tools like CRIU that >>>> rely on the soft-dirty mechanism for tracking memory changes. >>> >>> IIRC, false positives are not a problem. We get them all of the time >>> when merging VMAs etc. >> >> Right, Indeed. >> >>> So I am not sure if this here is really worth fixing. Soft-dirty is not, >>> and never will be false-positive free. >> >> Makes sense to me. It doesn’t seem worth the trouble to fix. Let’s go >> ahead and drop it. > > Yeah, I would prefer if we can just decouple soft-dirty from dirty > handling at some point. I recall I had a use case around > PageAnonExclusive at some point. Cool. I'll give it a try ;)