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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 7302EC433E1 for ; Thu, 20 Aug 2020 05:56:36 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 107F62076E for ; Thu, 20 Aug 2020 05:56:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 107F62076E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 655DE6B0087; Thu, 20 Aug 2020 01:56:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 605BF6B0089; Thu, 20 Aug 2020 01:56:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4F4286B008C; Thu, 20 Aug 2020 01:56:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0244.hostedemail.com [216.40.44.244]) by kanga.kvack.org (Postfix) with ESMTP id 37A4B6B0087 for ; Thu, 20 Aug 2020 01:56:35 -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 E1E9C1F1B for ; Thu, 20 Aug 2020 05:56:34 +0000 (UTC) X-FDA: 77169887508.24.ring66_2315f6d2702e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 9ECDB1A4A0 for ; Thu, 20 Aug 2020 05:56:34 +0000 (UTC) X-HE-Tag: ring66_2315f6d2702e X-Filterd-Recvd-Size: 8185 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf27.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 05:56:33 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8976CAAB0; Thu, 20 Aug 2020 05:56:59 +0000 (UTC) Date: Thu, 20 Aug 2020 07:56:30 +0200 From: Michal Hocko To: Suren Baghdasaryan Cc: 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, ebiederm@xmission.com, 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 Subject: Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary Message-ID: <20200820055630.GW5422@dhcp22.suse.cz> References: <20200820002053.1424000-1-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200820002053.1424000-1-surenb@google.com> X-Rspamd-Queue-Id: 9ECDB1A4A0 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: On Wed 19-08-20 17:20:53, Suren Baghdasaryan wrote: > 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. Yes this seems like a reasonable approach. Should we learn about a usecase which relies on this threading model we might need a more sophisticated synchronization but for now this sounds like good enough. > Fixes: 44a70adec910 ("mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj") > Reported-by: Tim Murray > Suggested-by: Michal Hocko > Signed-off-by: Suren Baghdasaryan Acked-by: Michal Hocko Thanks! > --- > fs/proc/base.c | 7 +++---- > include/linux/oom.h | 1 + > include/linux/sched/coredump.h | 1 + > kernel/fork.c | 9 +++++++++ > mm/oom_kill.c | 2 ++ > 5 files changed, 16 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; > > 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 */ > #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..9177a76bf840 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1403,6 +1403,15 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk) > if (clone_flags & CLONE_VM) { > mmget(oldmm); > mm = oldmm; > + if (!(clone_flags & CLONE_SIGHAND)) { > + /* We need to synchronize with __set_oom_adj */ > + mutex_lock(&oom_adj_lock); > + set_bit(MMF_PROC_SHARED, &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); > + } > goto good_mm; > } > > 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) > { > -- > 2.28.0.297.g1956fa8f8d-goog -- Michal Hocko SUSE Labs