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=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 435F6C433E2 for ; Tue, 15 Sep 2020 12:13:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C0A462078E for ; Tue, 15 Sep 2020 12:13:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C0A462078E 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 DDDE190002A; Tue, 15 Sep 2020 08:13:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D8F1190001D; Tue, 15 Sep 2020 08:13:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C7D9E90002A; Tue, 15 Sep 2020 08:13:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0024.hostedemail.com [216.40.44.24]) by kanga.kvack.org (Postfix) with ESMTP id B2A3890001D for ; Tue, 15 Sep 2020 08:13:32 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 674EE2479 for ; Tue, 15 Sep 2020 12:13:32 +0000 (UTC) X-FDA: 77265186264.18.form74_010564227111 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin18.hostedemail.com (Postfix) with ESMTP id 38257100EC682 for ; Tue, 15 Sep 2020 12:13:32 +0000 (UTC) X-HE-Tag: form74_010564227111 X-Filterd-Recvd-Size: 4522 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf23.hostedemail.com (Postfix) with ESMTP for ; Tue, 15 Sep 2020 12:13:31 +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 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> X-Rspamd-Queue-Id: 38257100EC682 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 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