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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E013C636D6 for ; Thu, 23 Feb 2023 15:00:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234805AbjBWPAH (ORCPT ); Thu, 23 Feb 2023 10:00:07 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233846AbjBWO74 (ORCPT ); Thu, 23 Feb 2023 09:59:56 -0500 Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A6699211D9 for ; Thu, 23 Feb 2023 06:59:47 -0800 (PST) Received: by mail-pl1-x634.google.com with SMTP id ko13so13842710plb.13 for ; Thu, 23 Feb 2023 06:59:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=k+yWMvIWvw3WCrNeIHfg2T45OrUG0bC11D4EFok9F+M=; b=EB6dxFuO49E9hfnx+Osyz4QjHI3/kf2CZqPTbL8bZbPI2QTYpJp+BuVJf6x9/Op3aS xof+1Uoax1p7nvbELL+hvfbo39TWfpBmEBoy9EpUsAQdrTSvZuTrHRoWXL0gdYKaEor+ FlUMT4ZM537FZvyLzQVS2uN0IxwQHFIi6aHEt02yLOvzx/nI4cU6h6Jhn6sPqf2zGz3q 7n1Fj4k/PR8q2dQfzWmocEZdEerzfVqSvdFp8in5t8rCq1veO/qkTc35xDsvKZ7O1cgU codFdh6jBnohjFOUx2BlZiCyA2YSs+IROp6V+lyMbfz4+T3nV1nwcz5dHnaW98oy8QVz yOZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=k+yWMvIWvw3WCrNeIHfg2T45OrUG0bC11D4EFok9F+M=; b=eRH4eCou+L577H7bTI7fP0pe9kgdoKvF5OeEzsnUoLldCgcb/7iUkxN92aCtmgsmzc iELE9OjbdoTGI7UG1BeJkdMGKo4Ew4Vjb3mVyr5IpMFPMXbx9VA3tuDYgUArqGw88q0F hPNFm8SUUtunGzMrZQgtXky2NmQ/JvSzxjB1Jw84XpIeHwYAT4CcZg37VjGPXUKRsqkv j0cFIfz5C+WRwU8oMAcUCbHZRW7+75Kqic6HI+nkYVbXxPNUS4fa4+XZUpbk1KpEUzLF vJgfdjtJO5bOiiIs+9q8zVrUuwwwEJ3tOpchHa66KlZ2sERokDDF1ywjkJd4HLnfM7kl zo0A== X-Gm-Message-State: AO0yUKX2guW0rfNvSDA+BIOIVqfD8nGJv/V3hvMIgBzqUlvTd+nZi+jK 5B6a3HzPMjd29c6cv3FbFqA= X-Google-Smtp-Source: AK7set/Qc2kRq6mVoIFJONVn7gWNZxeDHePlIGkq7CYhB6h9Zfh2pnK8s5XWdm4snMLVlByeQRXokw== X-Received: by 2002:a05:6a20:3d0c:b0:c7:1bac:6ef9 with SMTP id y12-20020a056a203d0c00b000c71bac6ef9mr12306390pzi.46.1677164386983; Thu, 23 Feb 2023 06:59:46 -0800 (PST) Received: from localhost ([2400:8902::f03c:93ff:fe27:642a]) by smtp.gmail.com with ESMTPSA id bm2-20020a056a00320200b005ac419804d5sm1703160pfb.98.2023.02.23.06.59.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Feb 2023 06:59:46 -0800 (PST) Date: Thu, 23 Feb 2023 14:59:34 +0000 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, michalechner92@googlemail.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v3 16/35] mm/mmap: write-lock VMAs before merging, splitting or expanding them Message-ID: References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-17-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 23, 2023 at 02:51:27PM +0000, Hyeonggon Yoo wrote: > On Wed, Feb 15, 2023 at 09:17:31PM -0800, Suren Baghdasaryan wrote: > > Decisions about whether VMAs can be merged, split or expanded must be > > made while VMAs are protected from the changes which can affect that > > decision. For example, merge_vma uses vma->anon_vma in its decision > > Did you mean vma_merge()? > > > whether the VMA can be merged. Meanwhile, page fault handler changes > > vma->anon_vma during COW operation. > > Write-lock all VMAs which might be affected by a merge or split operation > > before making decision how such operations should be performed. > > > > It doesn't make sense (to me) to update vma->anon_vma during COW fault. > > AFAIK children's vma->anon_vma is allocated during fork() and > page->anon_vma is updated on COW to reduce rmap walking because it's now > unshared, no? > > As patch 26 just falls back to mmap_lock if no anon_vma is set, > I think we can assume nothing updates vma->anon_vma (and its interval > tree) if we are holding mmap_lock in write mode. *Not interval tree, as it can be modified by other processes* > > Or am I missing something? > > -- > Regards, > Hyeonggon >