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=-6.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS autolearn=no 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 EBB10C433E1 for ; Wed, 26 Aug 2020 17:30:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C507C2075E for ; Wed, 26 Aug 2020 17:30:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726739AbgHZRaI (ORCPT ); Wed, 26 Aug 2020 13:30:08 -0400 Received: from mx2.suse.de ([195.135.220.15]:53140 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726802AbgHZRaF (ORCPT ); Wed, 26 Aug 2020 13:30:05 -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 43EE5AD83; Wed, 26 Aug 2020 17:30:32 +0000 (UTC) Date: Wed, 26 Aug 2020 19:29:53 +0200 From: Michal Hocko To: Johannes Weiner Cc: Xunlei Pang , Andrew Morton , Vladimir Davydov , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm: memcg: Fix memcg reclaim soft lockup Message-ID: <20200826172953.GT22869@dhcp22.suse.cz> References: <1598449622-108748-1-git-send-email-xlpang@linux.alibaba.com> <20200826164332.GB995045@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200826164332.GB995045@cmpxchg.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 26-08-20 12:43:32, Johannes Weiner wrote: > On Wed, Aug 26, 2020 at 09:47:02PM +0800, Xunlei Pang wrote: > > We've met softlockup with "CONFIG_PREEMPT_NONE=y", when > > the target memcg doesn't have any reclaimable memory. > > > > It can be easily reproduced as below: > > watchdog: BUG: soft lockup - CPU#0 stuck for 111s![memcg_test:2204] > > CPU: 0 PID: 2204 Comm: memcg_test Not tainted 5.9.0-rc2+ #12 > > Call Trace: > > shrink_lruvec+0x49f/0x640 > > shrink_node+0x2a6/0x6f0 > > do_try_to_free_pages+0xe9/0x3e0 > > try_to_free_mem_cgroup_pages+0xef/0x1f0 > > try_charge+0x2c1/0x750 > > mem_cgroup_charge+0xd7/0x240 > > __add_to_page_cache_locked+0x2fd/0x370 > > add_to_page_cache_lru+0x4a/0xc0 > > pagecache_get_page+0x10b/0x2f0 > > filemap_fault+0x661/0xad0 > > ext4_filemap_fault+0x2c/0x40 > > __do_fault+0x4d/0xf9 > > handle_mm_fault+0x1080/0x1790 > > > > It only happens on our 1-vcpu instances, because there's no chance > > for oom reaper to run to reclaim the to-be-killed process. > > > > Add cond_resched() at the upper shrink_node_memcgs() to solve this > > issue, and any other possible issue like meomry.min protection. > > > > Suggested-by: Michal Hocko > > Signed-off-by: Xunlei Pang > > This generally makes sense to me but really should have a comment: > > /* > * This loop can become CPU-bound when there are thousands > * of cgroups that aren't eligible for reclaim - either > * because they don't have any pages, or because their > * memory is explicitly protected. Avoid soft lockups. > */ > cond_resched(); > > The placement in the middle of the multi-part protection checks is a > bit odd too. It would be better to have it either at the top of the > loop, or at the end, by replacing the continues with goto next. Yes makes sense. I would stick it to the begining of the loop to make it stand out and make it obvious wrt code flow. -- Michal Hocko SUSE Labs