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=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 AA38CC433E1 for ; Thu, 20 Aug 2020 09:09:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5FF2E2078B for ; Thu, 20 Aug 2020 09:09:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5FF2E2078B 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 DAE3D6B0070; Thu, 20 Aug 2020 05:09:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D5F4F6B0072; Thu, 20 Aug 2020 05:09:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C76CC8D0001; Thu, 20 Aug 2020 05:09:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0054.hostedemail.com [216.40.44.54]) by kanga.kvack.org (Postfix) with ESMTP id B30476B0070 for ; Thu, 20 Aug 2020 05:09:04 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 522679892 for ; Thu, 20 Aug 2020 09:09:04 +0000 (UTC) X-FDA: 77170372608.06.eye63_2d0b3832702f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin06.hostedemail.com (Postfix) with ESMTP id 2C56C100584FC for ; Thu, 20 Aug 2020 09:09:04 +0000 (UTC) X-HE-Tag: eye63_2d0b3832702f X-Filterd-Recvd-Size: 8498 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf04.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 09:09:03 +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 5D107B761; Thu, 20 Aug 2020 09:09:29 +0000 (UTC) Date: Thu, 20 Aug 2020 11:09:01 +0200 From: Michal Hocko To: Christian Brauner Cc: Suren Baghdasaryan , 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: <20200820090901.GD5033@dhcp22.suse.cz> References: <20200820002053.1424000-1-surenb@google.com> <20200820084654.jdl6jqgxsga7orvf@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200820084654.jdl6jqgxsga7orvf@wittgenstein> X-Rspamd-Queue-Id: 2C56C100584FC 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: On Thu 20-08-20 10:46:54, Christian Brauner wrote: > On Wed, Aug 19, 2020 at 05:20:53PM -0700, 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. > > > > 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 > > --- > > 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); > > This seems fine. > > > + /* 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; > > But this seems wrong to me. > copy_signal() should be the only place where ->signal is set. Just from > a pure conceptual perspective. The copy_*() should be as self-contained > as possible imho. > Also, now I have to remember/look for two different locations where > oom_score_adj{_min} is initialized during fork. And this also creates a > dependency between copy_signal() and copy_mm() that doesn't need to be > there imho. I'm not a fan. Yes, this is not great but we will need it because the __set_oom_adj might happen between copy_signal and copy_mm. If that happens then __set_oom_adj misses this newly created task and so it will have a disagreeing oom_score_adj. -- Michal Hocko SUSE Labs