From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966877AbdEWIu7 (ORCPT ); Tue, 23 May 2017 04:50:59 -0400 Received: from terminus.zytor.com ([65.50.211.136]:57735 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762391AbdEWIuz (ORCPT ); Tue, 23 May 2017 04:50:55 -0400 Date: Tue, 23 May 2017 01:47:08 -0700 From: tip-bot for Vlastimil Babka Message-ID: Cc: vbabka@suse.cz, torvalds@linux-foundation.org, hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, riel@redhat.com, mgorman@techsingularity.net, peterz@infradead.org Reply-To: linux-kernel@vger.kernel.org, mingo@kernel.org, tglx@linutronix.de, hpa@zytor.com, torvalds@linux-foundation.org, vbabka@suse.cz, peterz@infradead.org, mgorman@techsingularity.net, riel@redhat.com In-Reply-To: <20170515131316.21909-1-vbabka@suse.cz> References: <20170515131316.21909-1-vbabka@suse.cz> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/numa: Use down_read_trylock() for the mmap_sem Git-Commit-ID: 8655d5497735b288f8a9b458bd22e7d1bf95bb61 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 8655d5497735b288f8a9b458bd22e7d1bf95bb61 Gitweb: http://git.kernel.org/tip/8655d5497735b288f8a9b458bd22e7d1bf95bb61 Author: Vlastimil Babka AuthorDate: Mon, 15 May 2017 15:13:16 +0200 Committer: Ingo Molnar CommitDate: Tue, 23 May 2017 10:01:34 +0200 sched/numa: Use down_read_trylock() for the mmap_sem A customer has reported a soft-lockup when running an intensive memory stress test, where the trace on multiple CPU's looks like this: RIP: 0010:[] [] native_queued_spin_lock_slowpath+0x10e/0x190 ... Call Trace: [] queued_spin_lock_slowpath+0x7/0xa [] change_protection_range+0x3b1/0x930 [] change_prot_numa+0x18/0x30 [] task_numa_work+0x1fe/0x310 [] task_work_run+0x72/0x90 Further investigation showed that the lock contention here is pmd_lock(). The task_numa_work() function makes sure that only one thread is let to perform the work in a single scan period (via cmpxchg), but if there's a thread with mmap_sem locked for writing for several periods, multiple threads in task_numa_work() can build up a convoy waiting for mmap_sem for read and then all get unblocked at once. This patch changes the down_read() to the trylock version, which prevents the build up. For a workload experiencing mmap_sem contention, it's probably better to postpone the NUMA balancing work anyway. This seems to have fixed the soft lockups involving pmd_lock(), which is in line with the convoy theory. Signed-off-by: Vlastimil Babka Signed-off-by: Peter Zijlstra (Intel) Acked-by: Rik van Riel Acked-by: Mel Gorman Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170515131316.21909-1-vbabka@suse.cz Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 219fe58..47a0c55 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2470,7 +2470,8 @@ void task_numa_work(struct callback_head *work) return; - down_read(&mm->mmap_sem); + if (!down_read_trylock(&mm->mmap_sem)) + return; vma = find_vma(mm, start); if (!vma) { reset_ptenuma_scan(p);