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 5D480C636CC for ; Fri, 17 Feb 2023 02:15:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A13396B0072; Thu, 16 Feb 2023 21:15:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 99B7A6B0073; Thu, 16 Feb 2023 21:15:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8155B6B0074; Thu, 16 Feb 2023 21:15:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 6D22C6B0072 for ; Thu, 16 Feb 2023 21:15:13 -0500 (EST) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 43EEF1612CF for ; Fri, 17 Feb 2023 02:15:13 +0000 (UTC) X-FDA: 80475166506.29.2497B44 Received: from mail-yw1-f180.google.com (mail-yw1-f180.google.com [209.85.128.180]) by imf05.hostedemail.com (Postfix) with ESMTP id 8DE5310001B for ; Fri, 17 Feb 2023 02:15:11 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=HZ1MbnjL; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf05.hostedemail.com: domain of surenb@google.com designates 209.85.128.180 as permitted sender) smtp.mailfrom=surenb@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1676600111; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=gIW9E+wxkNTINaEXAot3lldoZz6sgaV4NvNtgjJaTFE=; b=v5so4Ct/qO4+6Yez2mGiHQDZ7eHsNy3rLvWEGb0KiIfXdo5Az9KrKeKL282i8s4Y9mnxNH PERHdod4mHnBkt0Xj0YsJSyAcysd8+vptWVBLEGwSKl5SEZDg0AgZz8EPidzmfQAeitO6F J7ZAUcVESQjU6EfPdVYtE8zkq67zyhc= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=HZ1MbnjL; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf05.hostedemail.com: domain of surenb@google.com designates 209.85.128.180 as permitted sender) smtp.mailfrom=surenb@google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1676600111; a=rsa-sha256; cv=none; b=jJpirFnPu6/zIEWTnZCnfnlvgHR1eKsqXDBfgm30TlPPWtqz0QWjiP1pvrRXG8e9h+C8nL STdlVhH3oZqKVy6ASYMIftDbyu5t8OfJ5vZINKfYFm3vd//R+inRqyQ+IrXVl9a/DmAnNn chEkoaLapJPiPNSVSICeuGNEiv02H30= Received: by mail-yw1-f180.google.com with SMTP id 00721157ae682-501c3a414acso52377627b3.7 for ; Thu, 16 Feb 2023 18:15:11 -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=gIW9E+wxkNTINaEXAot3lldoZz6sgaV4NvNtgjJaTFE=; b=HZ1MbnjL/We5C6AX8xTKc/NqTWr1JbNL6JlhMYjY4MPeRhcx4XZI09qb39bGwvRHpn 8cDtil8U0r6ullafxJ+QwLrNcyZB/iYRlwQxWBWKusbbvKu5LjqUSwq9Ra4ShiIiGrEv AxeeaI71BN3x7atdH3dnzKmeE+EolPr5w0YLihfjx8Lqhfdtg4nJ/eIYXfAJrzuibZs7 cByt+UC1cn5tWYrIXSmdfIJG8w44wiSxOwaDq0TQPCM1gjyd36andjC6MWF3zwokrgru 63sqYZasEEiF/RtcTOEDIThAitqANjlx8nQcaAyiwezVllR+cWq9GK3mwpXFnbRC0O/W bLkw== 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=gIW9E+wxkNTINaEXAot3lldoZz6sgaV4NvNtgjJaTFE=; b=ckDCT/zNzb6EtOpgXsCXv/1tmbmonLMo66QtAQ/pokh4fSlSgrE+5tfcn+Qn+ZZpJy zw1RnGF/CContNMUE0Pn9fBnNLUDD0A7DCaanPFPxNDTr7r/VZ7HlO2FXKhKBm11omg7 raBaOcJHUgUIIAD+9sHcypyYbFYZoRzbjzLTAGwY1zjVm6JrYnkUrT49AE2RWCfsA2bD iwrjycBpEAsmB8nmj1I74HhSDca17iHsHMu1ETwfxpkSdWUUouNlrqveS5ClFjyPwrYz vzljw/5HepaMfzIp/2uuQ6cLV/VqmEVXg3MfAnaio2K9luQxnFKa8+5yenkEiM2R51au 8iRA== X-Gm-Message-State: AO0yUKX1sCswz6m+WoxRpbZeirz49+Ji4VakfZbu563EaQphcGNzkQ8c A3QxYYqF/eNmCEuoJV8YyZ/H4iPloOqERJXc8dMu4A== X-Google-Smtp-Source: AK7set9iDocdfaltT1vBZM1FfqGEUR3CgAtWXk18fjpJx7Nf/An2UuUbR7/i7tvhGQPyuOkqzQZqqs2JkP/rFvIUCdY= X-Received: by 2002:a81:4ed4:0:b0:506:6364:fda3 with SMTP id c203-20020a814ed4000000b005066364fda3mr971621ywb.72.1676600110454; Thu, 16 Feb 2023 18:15:10 -0800 (PST) MIME-Version: 1.0 References: <20230216051750.3125598-1-surenb@google.com> <20230216051750.3125598-27-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Thu, 16 Feb 2023 18:14:59 -0800 Message-ID: Subject: Re: [PATCH v3 26/35] mm: fall back to mmap_lock if vma->anon_vma is not yet set To: Matthew Wilcox 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, 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" X-Rspamd-Queue-Id: 8DE5310001B X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: hj4qjw8a84rc4dybpfa14yy5nok5wzqo X-HE-Tag: 1676600111-362409 X-HE-Meta: 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 +mJl5P2f zuKTQ7lOvnWoiR6SBdezKTDBeJLW4CdvQimK1HI6OyFnDGfNuZ5XFuzFg+PI/aF6Y452HC16azleooJw2srWa8k7GJJvCpqaYWQa6bcKmRVk5ukQLgvtYlBoe7VujnS8Qc57m28Jjnnb/g4DlDvkfu3sEYTJiXHDkp8oQXWV7O4BJdkUtk/+rpJZPy5fLKFsSSOxY3dlzGPHSvEMWCWR8mjmfqYZzmm3rUBAUbEdWSb5hSxUxyHJvwVSL8cJuB3UGWx7BDPKQ3rZn0YQSSRFekMhjFnk09AWdpAWZQcz2SofzX1t2XqVq5E5BMmynWV2lIsvbDa5zdJ/qr0roK0FkLYCdg7yHD1Iz2sUCrIXJnnzrnFJbiAu45W0RJw== 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: On Thu, Feb 16, 2023 at 11:43 AM Suren Baghdasaryan wrote: > > On Thu, Feb 16, 2023 at 7:44 AM Matthew Wilcox wrote: > > > > On Wed, Feb 15, 2023 at 09:17:41PM -0800, Suren Baghdasaryan wrote: > > > When vma->anon_vma is not set, page fault handler will set it by either > > > reusing anon_vma of an adjacent VMA if VMAs are compatible or by > > > allocating a new one. find_mergeable_anon_vma() walks VMA tree to find > > > a compatible adjacent VMA and that requires not only the faulting VMA > > > to be stable but also the tree structure and other VMAs inside that tree. > > > Therefore locking just the faulting VMA is not enough for this search. > > > Fall back to taking mmap_lock when vma->anon_vma is not set. This > > > situation happens only on the first page fault and should not affect > > > overall performance. > > > > I think I asked this before, but don't remember getting an aswer. > > Why do we defer setting anon_vma to the first fault? Why don't we > > set it up at mmap time? > > Yeah, I remember that conversation Matthew and I could not find the > definitive answer at the time. I'll look into that again or maybe > someone can answer it here. After looking into it again I'm still under the impression that vma->anon_vma is populated lazily (during the first page fault rather than at mmap time) to avoid doing extra work for areas which are never faulted. Though I might be missing some important detail here. > > In the end rather than changing that logic I decided to skip > vma->anon_vma==NULL cases because I measured them being less than > 0.01% of all page faults, so ROI from changing that would be quite > low. But I agree that the logic is weird and maybe we can improve > that. I will have to review that again when I'm working on eliminating > all these special cases we skip, like swap/userfaults/etc.