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,URIBL_BLOCKED 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 C530CC43461 for ; Tue, 15 Sep 2020 12:14:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9025C2078E for ; Tue, 15 Sep 2020 12:14:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726509AbgIOMOv (ORCPT ); Tue, 15 Sep 2020 08:14:51 -0400 Received: from mx2.suse.de ([195.135.220.15]:55676 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726183AbgIOMNc (ORCPT ); Tue, 15 Sep 2020 08:13:32 -0400 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 BD3CDB4F7; Tue, 15 Sep 2020 12:13:45 +0000 (UTC) Date: Tue, 15 Sep 2020 14:13:29 +0200 From: Michal Hocko To: zangchunxin@bytedance.com Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song Subject: Re: [PATCH v3] mm/vmscan: add a fatal signals check in drop_slab_node Message-ID: <20200915121329.GC4649@dhcp22.suse.cz> References: <20200915114001.79950-1-zangchunxin@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200915114001.79950-1-zangchunxin@bytedance.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 15-09-20 19:40:01, zangchunxin@bytedance.com wrote: > From: Chunxin Zang > > On our server, there are about 10k memcg in one machine. They use memory > very frequently. We have observed that drop_caches can take a > considerable amount of time, and can't stop it. > > There are two reasons: > 1. There is somebody constantly generating more objects to reclaim > on drop_caches, result the 'freed' always bigger than 10. > 2. The process has no chance to process signals. > > We can get the following info through 'ps': > > root:~# ps -aux | grep drop > root 357956 ... R Aug25 21119854:55 echo 3 > /proc/sys/vm/drop_caches > root 1771385 ... R Aug16 21146421:17 echo 3 > /proc/sys/vm/drop_caches > root 1986319 ... R 18:56 117:27 echo 3 > /proc/sys/vm/drop_caches > root 2002148 ... R Aug24 5720:39 echo 3 > /proc/sys/vm/drop_caches > root 2564666 ... R 18:59 113:58 echo 3 > /proc/sys/vm/drop_caches > root 2639347 ... R Sep03 2383:39 echo 3 > /proc/sys/vm/drop_caches > root 3904747 ... R 03:35 993:31 echo 3 > /proc/sys/vm/drop_caches > root 4016780 ... R Aug21 7882:18 echo 3 > /proc/sys/vm/drop_caches > > Use bpftrace follow 'freed' value in drop_slab_node: > > root:~# bpftrace -e 'kprobe:drop_slab_node+70 {@ret=hist(reg("bp")); }' > Attaching 1 probe... > ^B^C > > @ret: > [64, 128) 1 | | > [128, 256) 28 | | > [256, 512) 107 |@ | > [512, 1K) 298 |@@@ | > [1K, 2K) 613 |@@@@@@@ | > [2K, 4K) 4435 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@| > [4K, 8K) 442 |@@@@@ | > [8K, 16K) 299 |@@@ | > [16K, 32K) 100 |@ | > [32K, 64K) 139 |@ | > [64K, 128K) 56 | | > [128K, 256K) 26 | | > [256K, 512K) 2 | | I am not sure this is very helpful for this patch but whatever. > We need one path to stop the process. I would use the following instead " Add a bail out on the fatal signals in the main loop so that the operation can be terminated by userspace. " > > Signed-off-by: Chunxin Zang > Signed-off-by: Muchun Song Acked-by: Michal Hocko > --- > > changelogs in v3: > 1) update the description of the patch. > v2 named: mm/vmscan: fix infinite loop in drop_slab_node > > changelogs in v2: > 1) via check fatal signal break loop. > > mm/vmscan.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index b6d84326bdf2..6b2b5d420510 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -704,6 +704,9 @@ void drop_slab_node(int nid) > do { > struct mem_cgroup *memcg = NULL; > > + if (signal_pending(current)) > + return; > + > freed = 0; > memcg = mem_cgroup_iter(NULL, NULL, NULL); > do { > -- > 2.11.0 > -- Michal Hocko SUSE Labs