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=-9.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 5308DC433DF for ; Tue, 25 Aug 2020 16:38:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E7E2A20825 for ; Tue, 25 Aug 2020 16:38:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E7E2A20825 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 35F928E0006; Tue, 25 Aug 2020 12:38:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 30FF28D0002; Tue, 25 Aug 2020 12:38:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1FE988E0006; Tue, 25 Aug 2020 12:38:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0224.hostedemail.com [216.40.44.224]) by kanga.kvack.org (Postfix) with ESMTP id 0B7A58D0002 for ; Tue, 25 Aug 2020 12:38:10 -0400 (EDT) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id BAD831DE9 for ; Tue, 25 Aug 2020 16:38:09 +0000 (UTC) X-FDA: 77189648298.24.lead09_1304d652705d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 8C3771A4A0 for ; Tue, 25 Aug 2020 16:38:09 +0000 (UTC) X-HE-Tag: lead09_1304d652705d X-Filterd-Recvd-Size: 12277 Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by imf37.hostedemail.com (Postfix) with ESMTP for ; Tue, 25 Aug 2020 16:38:08 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]) by out02.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1kAbxL-00H0Y9-3q; Tue, 25 Aug 2020 10:37:55 -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 1kAbxJ-0006FB-SK; Tue, 25 Aug 2020 10:37:54 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Suren Baghdasaryan Cc: mhocko@suse.com, 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, stable@vger.kernel.org, linux-mm@kvack.org, Michal Hocko References: <20200824153036.3201505-1-surenb@google.com> Date: Tue, 25 Aug 2020 11:34:11 -0500 In-Reply-To: <20200824153036.3201505-1-surenb@google.com> (Suren Baghdasaryan's message of "Mon, 24 Aug 2020 08:30:36 -0700") Message-ID: <87imd6n0qk.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=1kAbxJ-0006FB-SK;;;mid=<87imd6n0qk.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX19ivDnjXPoNOaQ5Sbo9GtQ7QzaAzyR6xy4= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v2 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: 8C3771A4A0 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: 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 && !CLONE_THREAD && !CLONE_VFORK). 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. The combination of > (CLONE_VM && !CLONE_THREAD) is rarely used except for the case of vfork(). > To prevent performance regressions of vfork(), we skip taking oom_adj_lock > and setting MMF_PROC_SHARED when CLONE_VFORK is specified. 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 && !CLONE_THREAD && !CLONE_VFORK) being > quite rare, the regression is gone after the change is applied. This patch still makes my head hurt. The obvious wrong things I have mentioned below. > Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj") > Reported-by: Tim Murray > Debugged-by: Minchan Kim > Suggested-by: Michal Hocko > Signed-off-by: Suren Baghdasaryan > --- > > v2: > - Implemented proposal from Michal Hocko in: > https://lore.kernel.org/linux-fsdevel/20200820124109.GI5033@dhcp22.suse.cz/ > - Updated description to reflect the change > > v1: > - https://lore.kernel.org/linux-mm/20200820002053.1424000-1-surenb@google.com/ > > fs/proc/base.c | 7 +++---- > include/linux/oom.h | 1 + > include/linux/sched/coredump.h | 1 + > kernel/fork.c | 21 +++++++++++++++++++++ > mm/oom_kill.c | 2 ++ > 5 files changed, 28 insertions(+), 4 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 617db4e0faa0..cff1a58a236c 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -1055,7 +1055,6 @@ static ssize_t oom_adj_read(struct file *file, char __user *buf, size_t count, > > static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > { > - static DEFINE_MUTEX(oom_adj_mutex); > struct mm_struct *mm = NULL; > struct task_struct *task; > int err = 0; > @@ -1064,7 +1063,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > if (!task) > return -ESRCH; > > - mutex_lock(&oom_adj_mutex); > + mutex_lock(&oom_adj_lock); > if (legacy) { > if (oom_adj < task->signal->oom_score_adj && > !capable(CAP_SYS_RESOURCE)) { > @@ -1095,7 +1094,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > struct task_struct *p = find_lock_task_mm(task); > > if (p) { > - if (atomic_read(&p->mm->mm_users) > 1) { > + if (test_bit(MMF_PROC_SHARED, &p->mm->flags)) { > mm = p->mm; > mmgrab(mm); > } > @@ -1132,7 +1131,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > mmdrop(mm); > } > err_unlock: > - mutex_unlock(&oom_adj_mutex); > + mutex_unlock(&oom_adj_lock); > put_task_struct(task); > return err; > } > diff --git a/include/linux/oom.h b/include/linux/oom.h > index f022f581ac29..861f22bd4706 100644 > --- a/include/linux/oom.h > +++ b/include/linux/oom.h > @@ -55,6 +55,7 @@ struct oom_control { > }; > > extern struct mutex oom_lock; > +extern struct mutex oom_adj_lock; ^^^^^^^^^^^^^^ I understand moving this lock by why renaming it? > static inline void set_current_oom_origin(void) > { > diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h > index ecdc6542070f..070629b722df 100644 > --- a/include/linux/sched/coredump.h > +++ b/include/linux/sched/coredump.h > @@ -72,6 +72,7 @@ static inline int get_dumpable(struct mm_struct *mm) > #define MMF_DISABLE_THP 24 /* disable THP for all VMAs */ > #define MMF_OOM_VICTIM 25 /* mm is the oom victim */ > #define MMF_OOM_REAP_QUEUED 26 /* mm was queued for oom_reaper */ > +#define MMF_PROC_SHARED 27 /* mm is shared while sighand is not */ ^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Arguably this is misnamed MMF_MULTIPROCESS is probably better. The comment is definitely wrong. > #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) > > #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ > diff --git a/kernel/fork.c b/kernel/fork.c > index 4d32190861bd..6fce8ffa9b8b 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1809,6 +1809,25 @@ static __always_inline void delayed_free_task(struct task_struct *tsk) > free_task(tsk); > } > > +static void copy_oom_score_adj(u64 clone_flags, struct task_struct *tsk) > +{ > + /* Skip if kernel thread */ > + if (!tsk->mm) > + return; > + > + /* Skip if spawning a thread or using vfork */ > + if ((clone_flags & (CLONE_VM | CLONE_THREAD | CLONE_VFORK)) != CLONE_VM) > + return; > + > + /* We need to synchronize with __set_oom_adj */ > + mutex_lock(&oom_adj_lock); > + set_bit(MMF_PROC_SHARED, &tsk->mm->flags); > + /* Update the values in case they were changed after copy_signal */ > + tsk->signal->oom_score_adj = current->signal->oom_score_adj; > + tsk->signal->oom_score_adj_min = current->signal->oom_score_adj_min; > + mutex_unlock(&oom_adj_lock); The copying and the setting of a bit on a mm should be logically separate things. This really makes my head hurt because the functionality is not separated out. I don't have a clue how we could maintain this copy_oom_score_adj function. > +} > + > /* > * This creates a new process as a copy of the old one, > * but does not actually start it yet. > @@ -2281,6 +2300,8 @@ static __latent_entropy struct task_struct *copy_process( > trace_task_newtask(p, clone_flags); > uprobe_copy_process(p, clone_flags); > > + copy_oom_score_adj(clone_flags, p); > + > return p; > > bad_fork_cancel_cgroup: > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index e90f25d6385d..c22f07c986cb 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -64,6 +64,8 @@ int sysctl_oom_dump_tasks = 1; > * and mark_oom_victim > */ > DEFINE_MUTEX(oom_lock); > +/* Serializes oom_score_adj and oom_score_adj_min updates */ > +DEFINE_MUTEX(oom_adj_lock); > > static inline bool is_memcg_oom(struct oom_control *oc) > { Eric