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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0DC0FC433E1 for ; Thu, 20 Aug 2020 12:58:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A3FF020658 for ; Thu, 20 Aug 2020 12:58:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A3FF020658 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3BDAE8D0003; Thu, 20 Aug 2020 08:58:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 36E818D0001; Thu, 20 Aug 2020 08:58:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 283E98D0003; Thu, 20 Aug 2020 08:58:34 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0175.hostedemail.com [216.40.44.175]) by kanga.kvack.org (Postfix) with ESMTP id 125B28D0001 for ; Thu, 20 Aug 2020 08:58:34 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id B80B0180AD801 for ; Thu, 20 Aug 2020 12:58:33 +0000 (UTC) X-FDA: 77170950906.19.actor99_420602127030 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin19.hostedemail.com (Postfix) with ESMTP id 8224B1AD1B3 for ; Thu, 20 Aug 2020 12:58:33 +0000 (UTC) X-HE-Tag: actor99_420602127030 X-Filterd-Recvd-Size: 7833 Received: from out01.mta.xmission.com (out01.mta.xmission.com [166.70.13.231]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 12:58:32 +0000 (UTC) Received: from in02.mta.xmission.com ([166.70.13.52]) by out01.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1k8k97-00AeLu-MA; Thu, 20 Aug 2020 06:58:21 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1k8k96-0001vI-Nm; Thu, 20 Aug 2020 06:58:21 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Michal Hocko Cc: Suren Baghdasaryan , christian.brauner@ubuntu.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, esyr@redhat.com, christian@kellner.me, areber@redhat.com, shakeelb@google.com, cyphar@cyphar.com, oleg@redhat.com, adobriyan@gmail.com, akpm@linux-foundation.org, gladkov.alexey@gmail.com, walken@google.com, daniel.m.jordan@oracle.com, avagin@gmail.com, bernd.edlinger@hotmail.de, john.johansen@canonical.com, laoar.shao@gmail.com, timmurray@google.com, minchan@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20200820002053.1424000-1-surenb@google.com> <87zh6pxzq6.fsf@x220.int.ebiederm.org> <20200820124241.GJ5033@dhcp22.suse.cz> <87lfi9xz7y.fsf@x220.int.ebiederm.org> Date: Thu, 20 Aug 2020 07:54:44 -0500 In-Reply-To: <87lfi9xz7y.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Thu, 20 Aug 2020 07:45:37 -0500") Message-ID: <87d03lxysr.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1k8k96-0001vI-Nm;;;mid=<87d03lxysr.fsf@x220.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19E902mpzZ/0RJGbVRpvQ/hKnf/i0hasRo= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) X-Rspamd-Queue-Id: 8224B1AD1B3 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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: ebiederm@xmission.com (Eric W. Biederman) writes: 2> Michal Hocko writes: > >> On Thu 20-08-20 07:34:41, Eric W. Biederman wrote: >>> Suren Baghdasaryan writes: >>> >>> > Currently __set_oom_adj loops through all processes in the system to >>> > keep oom_score_adj and oom_score_adj_min in sync between processes >>> > sharing their mm. This is done for any task with more that one mm_users, >>> > which includes processes with multiple threads (sharing mm and signals). >>> > However for such processes the loop is unnecessary because their signal >>> > structure is shared as well. >>> > Android updates oom_score_adj whenever a tasks changes its role >>> > (background/foreground/...) or binds to/unbinds from a service, making >>> > it more/less important. Such operation can happen frequently. >>> > We noticed that updates to oom_score_adj became more expensive and after >>> > further investigation found out that the patch mentioned in "Fixes" >>> > introduced a regression. Using Pixel 4 with a typical Android workload, >>> > write time to oom_score_adj increased from ~3.57us to ~362us. Moreover >>> > this regression linearly depends on the number of multi-threaded >>> > processes running on the system. >>> > Mark the mm with a new MMF_PROC_SHARED flag bit when task is created with >>> > CLONE_VM and !CLONE_SIGHAND. Change __set_oom_adj to use MMF_PROC_SHARED >>> > instead of mm_users to decide whether oom_score_adj update should be >>> > synchronized between multiple processes. To prevent races between clone() >>> > and __set_oom_adj(), when oom_score_adj of the process being cloned might >>> > be modified from userspace, we use oom_adj_mutex. Its scope is changed to >>> > global and it is renamed into oom_adj_lock for naming consistency with >>> > oom_lock. Since the combination of CLONE_VM and !CLONE_SIGHAND is rarely >>> > used the additional mutex lock in that path of the clone() syscall should >>> > not affect its overall performance. Clearing the MMF_PROC_SHARED flag >>> > (when the last process sharing the mm exits) is left out of this patch to >>> > keep it simple and because it is believed that this threading model is >>> > rare. Should there ever be a need for optimizing that case as well, it >>> > can be done by hooking into the exit path, likely following the >>> > mm_update_next_owner pattern. >>> > With the combination of CLONE_VM and !CLONE_SIGHAND being quite rare, the >>> > regression is gone after the change is applied. >>> >>> So I am confused. >>> >>> Is there any reason why we don't simply move signal->oom_score_adj to >>> mm->oom_score_adj and call it a day? >> >> Yes. Please read through 44a70adec910 ("mm, oom_adj: make sure processes >> sharing mm have same view of oom_score_adj") > > That explains why the scores are synchronized. > > It doesn't explain why we don't do the much simpler thing and move > oom_score_adj from signal_struct to mm_struct. Which is my question. > > Why not put the score where we need it to ensure that the oom score > is always synchronized? AKA on the mm_struct, not the signal_struct. Apologies. That 44a70adec910 does describe that some people have seen vfork users set oom_score. No details unfortunately. I will skip the part where posix calls this undefined behavior. It breaks userspace to change. It still seems like the code should be able to buffer oom_adj during vfork, and only move the value onto mm_struct during exec. Eric