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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2864BC3ABB2 for ; Fri, 30 May 2025 07:15:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BC7D36B0089; Fri, 30 May 2025 03:15:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B9FD46B008A; Fri, 30 May 2025 03:15:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A8DEC6B008C; Fri, 30 May 2025 03:15:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 8A7116B0089 for ; Fri, 30 May 2025 03:15:56 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id DDC47828DC for ; Fri, 30 May 2025 07:15:55 +0000 (UTC) X-FDA: 83498714670.26.668AD07 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) by imf12.hostedemail.com (Postfix) with ESMTP id 7C0B240004 for ; Fri, 30 May 2025 07:15:53 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=oBbrXNvT; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="9OD/Zc0w"; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=oBbrXNvT; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="9OD/Zc0w"; spf=pass (imf12.hostedemail.com: domain of vbabka@suse.cz designates 195.135.223.131 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1748589353; 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=uzU19k1ECLHjrvkeXuOD+PC+beRlg03ZHwC8d7LjQWg=; b=RmmzQtDWQN0phYhXjyGH+102CfWhnUwlf91WTggzPdet/+M95E+KTz6rYS+wB/qf/ufjO8 sjkRC07IztpU0PEcsEEBhbTGqII01DJYKl3pBWsuIamOhvrMpqilYD+IZP0paNjoGcjYdZ 98yXrYv2KHi6p1IHl4Fk8n0LyKoApfw= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=oBbrXNvT; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="9OD/Zc0w"; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=oBbrXNvT; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b="9OD/Zc0w"; spf=pass (imf12.hostedemail.com: domain of vbabka@suse.cz designates 195.135.223.131 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1748589353; a=rsa-sha256; cv=none; b=47P5rJA5fUBbH6DEFzW4MWDLTGnkJ92W7xHUTJcm3In9hNQDlsQtF9NMxWWuHLcBpAm8za DYtqlBVIuxYslDAUL+Kkk2lAdrFzhFmOaF1iTcxZdPoCSggFOk4uY4JBrQGsYZQyM7cNp0 RVIXnoQNOXh9xASywf+fQjdo0xy6hFg= Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id A49AF1F7A1; Fri, 30 May 2025 07:15:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1748589351; h=from:from:reply-to: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:autocrypt:autocrypt; bh=uzU19k1ECLHjrvkeXuOD+PC+beRlg03ZHwC8d7LjQWg=; b=oBbrXNvT2xBNFjpKCbW13YHP4O66WtaiTyPNKlnuc5QcBuF4n+TcsqWcbcPb4nwo1a2jC6 1C1SrGTPcNCN7IH3f4mTqvPbTXqogrgCxf56lmABQO7PgEaqPgxP13QXHIM5J6U4W+fjYs b4sx+5gytVsbJLWJUQecvMjY+JSgh1w= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1748589351; h=from:from:reply-to: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:autocrypt:autocrypt; bh=uzU19k1ECLHjrvkeXuOD+PC+beRlg03ZHwC8d7LjQWg=; b=9OD/Zc0wTvD0qN2XodBjaOf/qYa0n0OKAYU0m6GtrS7ZK435G9v4pzPmvuueiYHx8fJI/A 7lXqe5U+gx0WHYDQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1748589351; h=from:from:reply-to: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:autocrypt:autocrypt; bh=uzU19k1ECLHjrvkeXuOD+PC+beRlg03ZHwC8d7LjQWg=; b=oBbrXNvT2xBNFjpKCbW13YHP4O66WtaiTyPNKlnuc5QcBuF4n+TcsqWcbcPb4nwo1a2jC6 1C1SrGTPcNCN7IH3f4mTqvPbTXqogrgCxf56lmABQO7PgEaqPgxP13QXHIM5J6U4W+fjYs b4sx+5gytVsbJLWJUQecvMjY+JSgh1w= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1748589351; h=from:from:reply-to: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:autocrypt:autocrypt; bh=uzU19k1ECLHjrvkeXuOD+PC+beRlg03ZHwC8d7LjQWg=; b=9OD/Zc0wTvD0qN2XodBjaOf/qYa0n0OKAYU0m6GtrS7ZK435G9v4pzPmvuueiYHx8fJI/A 7lXqe5U+gx0WHYDQ== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 84BD8132D8; Fri, 30 May 2025 07:15:51 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Lw3OHydbOWhcSwAAD6G6ig (envelope-from ); Fri, 30 May 2025 07:15:51 +0000 Message-ID: Date: Fri, 30 May 2025 09:15:51 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/4] mm: prevent KSM from breaking VMA merging for new VMAs To: Lorenzo Stoakes , Andrew Morton Cc: Alexander Viro , Christian Brauner , Jan Kara , "Liam R . Howlett" , Jann Horn , Pedro Falcato , David Hildenbrand , Xu Xin , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Stefan Roesch References: <3ba660af716d87a18ca5b4e635f2101edeb56340.1748537921.git.lorenzo.stoakes@oracle.com> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <3ba660af716d87a18ca5b4e635f2101edeb56340.1748537921.git.lorenzo.stoakes@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 1ukay47tmsriwgobgww4mfm7fj78n51x X-Rspamd-Queue-Id: 7C0B240004 X-Rspamd-Server: rspam11 X-HE-Tag: 1748589353-12524 X-HE-Meta: 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 Nz1mOrol /SD+3OM+P5FNW16XsHZxqnnCzDp5HtcIHn/J+IcFzk41fUc11Q58u1ud9YEw07ZduHQH+GO1BrUZgJQqCySPoQTm4KpuhmSq9ZROTbhCBe9aprF48tuC5F5Tvlt1nL2GfK+9fLh8a+2Klzls7WMfSilrJJ6XNgbT2a+qe8lmy8gfgAyyJ8jWlOLpo9zMqAIiIo7XuoQiZI6bCUQIypN8lTWylc+ZsY2gB4fMQBKJY2rwP64ozs2GDv8IeD1yAI2xv7e3ChCKJJ9doEtbmAFJowz9jR57oufMqIBvED0DRYa6F3jaTwTAnlsTKmM9qsp7VSnj86qwiQoNeJw1yXr+nA1tOgQ== 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 5/29/25 19:15, Lorenzo Stoakes wrote: > If a user wishes to enable KSM mergeability for an entire process and all > fork/exec'd processes that come after it, they use the prctl() > PR_SET_MEMORY_MERGE operation. > > This defaults all newly mapped VMAs to have the VM_MERGEABLE VMA flag set > (in order to indicate they are KSM mergeable), as well as setting this flag > for all existing VMAs and propagating this across fork/exec. > > However it also breaks VMA merging for new VMAs, both in the process and > all forked (and fork/exec'd) child processes. > > This is because when a new mapping is proposed, the flags specified will > never have VM_MERGEABLE set. However all adjacent VMAs will already have > VM_MERGEABLE set, rendering VMAs unmergeable by default. > > To work around this, we try to set the VM_MERGEABLE flag prior to > attempting a merge. In the case of brk() this can always be done. > > However on mmap() things are more complicated - while KSM is not supported > for MAP_SHARED file-backed mappings, it is supported for MAP_PRIVATE > file-backed mappings. > > These mappings may have deprecated .mmap() callbacks specified which could, > in theory, adjust flags and thus KSM eligibility. > > So we check to determine whether this is possible. If not, we set > VM_MERGEABLE prior to the merge attempt on mmap(), otherwise we retain the > previous behaviour. > > This fixes VMA merging for all new anonymous mappings, which covers the > majority of real-world cases, so we should see a significant improvement in > VMA mergeability. > > For MAP_PRIVATE file-backed mappings, those which implement the > .mmap_prepare() hook and shmem are both known to be safe, so we allow > these, disallowing all other cases. > > Also add stubs for newly introduced function invocations to VMA userland > testing. > > Signed-off-by: Lorenzo Stoakes > Fixes: d7597f59d1d3 ("mm: add new api to enable ksm per process") # please no backport! > Reviewed-by: Chengming Zhou > Acked-by: David Hildenbrand > Reviewed-by: Liam R. Howlett The commit log is much clearer to me now, thanks :) Reviewed-by: Vlastimil Babka