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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 2DE72C433DF for ; Thu, 20 Aug 2020 12:49:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id EC27B2086A for ; Thu, 20 Aug 2020 12:49:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EC27B2086A 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 743EF8D000D; Thu, 20 Aug 2020 08:49:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 71AE88D0001; Thu, 20 Aug 2020 08:49:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6305C8D000D; Thu, 20 Aug 2020 08:49:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0076.hostedemail.com [216.40.44.76]) by kanga.kvack.org (Postfix) with ESMTP id 4BA228D0001 for ; Thu, 20 Aug 2020 08:49:28 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 029078248047 for ; Thu, 20 Aug 2020 12:49:28 +0000 (UTC) X-FDA: 77170928016.29.worm60_130e8e727030 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin29.hostedemail.com (Postfix) with ESMTP id BE8C118086E3F for ; Thu, 20 Aug 2020 12:49:27 +0000 (UTC) X-HE-Tag: worm60_130e8e727030 X-Filterd-Recvd-Size: 7294 Received: from out01.mta.xmission.com (out01.mta.xmission.com [166.70.13.231]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 12:49:27 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1k8k0I-00Adm1-K2; Thu, 20 Aug 2020 06:49:14 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1k8k0H-0004wa-Os; Thu, 20 Aug 2020 06:49:14 -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> Date: Thu, 20 Aug 2020 07:45:37 -0500 In-Reply-To: <20200820124241.GJ5033@dhcp22.suse.cz> (Michal Hocko's message of "Thu, 20 Aug 2020 14:42:41 +0200") Message-ID: <87lfi9xz7y.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=1k8k0H-0004wa-Os;;;mid=<87lfi9xz7y.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+DAdP7WXJ3+fqaabHe/txON167hJBjJH8= 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 in01.mta.xmission.com) X-Rspamd-Queue-Id: BE8C118086E3F X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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: 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. Eric