From patchwork Thu Aug 20 00:20:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 11725229 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 34BDF14E3 for ; Thu, 20 Aug 2020 00:21:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 172EC207FB for ; Thu, 20 Aug 2020 00:21:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="wMrGHODL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726871AbgHTAVG (ORCPT ); Wed, 19 Aug 2020 20:21:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726751AbgHTAVF (ORCPT ); Wed, 19 Aug 2020 20:21:05 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 029ACC061757 for ; Wed, 19 Aug 2020 17:21:04 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id o8so351078ybg.16 for ; Wed, 19 Aug 2020 17:21:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=Vnv0SMqgJcbIgs/QdGGWw4qUOL4tuoTWF08V7z/H2vQ=; b=wMrGHODLvxAB04FZ88TjDQYIFXykD4qua/0Y7R7daZ3sfYgVqTTioE5finV49SYUg0 z8OWYO1rTaTxecrbi3B85yr745b2LCUgGOuka435aXVNSXU9ALNyseFk/IVUoBnItzCa mFAeEIAb8oKIKWspSBzX19/soN9ERBQIrv+zEhfBi+GtPr+d+qVBOQiZ5IRNZB71PWOC QcVRJNELwF7hafZYPUD/JEtBSMN2zahu9R8lec6CUC0/WYdQ3mdV7//bGBJllbI7CTmF G10m2lmMEGQNqi35P2ruQKAoSzP7VvcadM/OgHPKKK0r3p15hF0wPT+S0kYom+EEOopc HNvQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=Vnv0SMqgJcbIgs/QdGGWw4qUOL4tuoTWF08V7z/H2vQ=; b=Q9pOhWxNlQde/yFMBvQwzFRdKKbDtzvUFHxQ/qZEL8UG3cGB3kQbt2NFkXvyAoBJP0 h6y+DMspAfvYkMIVpQlSN1UvKgcAm58y9HgbSRM28WwaWXVpREIMeYCJRWJV5EW4kWgu OylqHker1z4ILQRFzqF3ohoqgR6BwwuzH0+Ul1Z+G2LPAO3pQY79ErNdklSxuxsugHhd KDqDSWQTC/PtAesg6l1AACpNdnKu/h4w66rjOVoqYRXiose69V6Hpfd8FJbdo+O+Amw8 /gQyJ6rgFWInrOc+d8avXoo2MGGTNy+zeQejlLzh0gHamQSSLPt1/GGLMHSG2HsGoUbh nz9g== X-Gm-Message-State: AOAM531IhMyKz4kTKE9xmiazwOZ4meh4f9mmg/nmjzXYMeXSQ6T7uolz YrJSdeULRlsRp+Y1gqH2omoyr/Pb14E= X-Google-Smtp-Source: ABdhPJxWtvtuuALIVhHDzFDuamSO63tCHSlDXg9xIHnfvJjwkI+jWf/ctIuA00SYC2emSgj96QX5qm8xqZo= X-Received: from surenb1.mtv.corp.google.com ([2620:15c:211:0:f693:9fff:fef4:2055]) (user=surenb job=sendgmr) by 2002:a25:db8f:: with SMTP id g137mr1287656ybf.489.1597882864112; Wed, 19 Aug 2020 17:21:04 -0700 (PDT) Date: Wed, 19 Aug 2020 17:20:53 -0700 Message-Id: <20200820002053.1424000-1-surenb@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.28.0.297.g1956fa8f8d-goog Subject: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary From: Suren Baghdasaryan To: surenb@google.com 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, 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, Michal Hocko Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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 Acked-by: Michal Hocko --- 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) {