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 60D1BC636D6 for ; Thu, 23 Feb 2023 17:46:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230255AbjBWRqX (ORCPT ); Thu, 23 Feb 2023 12:46:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230257AbjBWRqV (ORCPT ); Thu, 23 Feb 2023 12:46:21 -0500 Received: from mail-yw1-x112b.google.com (mail-yw1-x112b.google.com [IPv6:2607:f8b0:4864:20::112b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D89DC584A6 for ; Thu, 23 Feb 2023 09:46:18 -0800 (PST) Received: by mail-yw1-x112b.google.com with SMTP id 00721157ae682-536bbe5f888so208679117b3.8 for ; Thu, 23 Feb 2023 09:46:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=g/PLDPGKQjPZMyA7q+2mFnv6mahBdE0bikjr2yluVPY=; b=dummwTyKyVw0SoCKQB2T+CwBI/Ypb4Xjjntbgjy5yY3C5JfegBtvOFcckYNV17WdQ/ 0w5jao6F1lAd1zF6E9RI9/RWGb80R3PDgmBk2m8yqC+Gi9Cz8dqE6Quoai9BJdhJlqEh HXWjKep0uNLo6oQwpJ0si4E5CdSInQ6nVrYPpOZOZDmYeky4HyVGIjYgVtIRp21yjlXY GGlDKZIvbQYER09r+RZ/9BDfYBpNR1R7LQbtmEy4HPIjt4ErWpQfPwxeLOIuF7azgaN9 TZCm0VAiYi4HMUn+5S8/JEaDBL3nNNe95Tqa3VX6huByAmE5cf905UXPLAp2GPZwk+ll sIgw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=g/PLDPGKQjPZMyA7q+2mFnv6mahBdE0bikjr2yluVPY=; b=LYUOwrt5EjDzHMZM0kBjomLO/zmLXLZGPfqA9ObK3uI7szXt7/WBaJYf0dVonYY7uc sd57YXrDQuDapyw2I1sbyBmoj3PELiwocgidZ18zeqWEPXwxOtNbxRho5u7WEQDBOC0g cB6LAHgQIla4jKc2TeGAIDead3prFjL/gllmOcCurZFnUg5obyL1QunDQA7OVJqC9CxK BOxRJ7meK4orcQkgxuIdTPilDQUM2rQnNYCCbvAN3ET5L2sogd6D0FAu7o4ot6rt17YS ktZz8DRMp1dJpCQDkzBlvxs2r1RMIPW8/hDNCRcCdJOn3U4DCR38+NUIZCy8We4mEh2C O+Cg== X-Gm-Message-State: AO0yUKU5++KTEUrJS2FXNlsz7OvaUwrS5Ob+yfmdhWeNyAdZ1Fif76nN a0P1YEWVBGnf89ol256L5dwDivSObbW16pLvB66xzw== X-Google-Smtp-Source: AK7set8VspgWW+dqkUupWcrMtXnPa8I+wv5kJWT4xioj+Je37AbwwoY0FONlPTo7MjbvDCQNHSJjmEXD8ltyQIw5ZGk= X-Received: by 2002:a81:b71b:0:b0:533:8f19:4576 with SMTP id v27-20020a81b71b000000b005338f194576mr2731678ywh.0.1677174377752; Thu, 23 Feb 2023 09:46:17 -0800 (PST) MIME-Version: 1.0 References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-17-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Thu, 23 Feb 2023 09:46:06 -0800 Message-ID: Subject: Re: [PATCH v3 16/35] mm/mmap: write-lock VMAs before merging, splitting or expanding them To: Hyeonggon Yoo <42.hyeyoo@gmail.com> 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 23, 2023 at 6:51 AM Hyeonggon Yoo <42.hyeyoo@gmail.com> 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()? Correct. > > > 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. > > Or am I missing something? No, I think you are right. Patch 26 was added in the later versions of this patchset and at the time this patch was written vma->anon_vma could change during page fault handling under only per-VMA lock protection. So, this patch can be simplified. We still want to prevent concurrent page faults while VMA is being merged or split (simply because par-VMA lock that page fault handler holds might become the wrong one if the VMA is split or merged from under it) but the timing of taking per-VMA lock does not have to be *before* can_vma_merge_{before|after}. Does that make sense? > > -- > Regards, > Hyeonggon > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >