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=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 218C9C55185 for ; Wed, 22 Apr 2020 12:54:31 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B92A020857 for ; Wed, 22 Apr 2020 12:54:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=cmpxchg-org.20150623.gappssmtp.com header.i=@cmpxchg-org.20150623.gappssmtp.com header.b="f7lwEsYn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B92A020857 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=cmpxchg.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2DD6F8E001B; Wed, 22 Apr 2020 08:54:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 28D7B8E0003; Wed, 22 Apr 2020 08:54:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1A3CC8E001B; Wed, 22 Apr 2020 08:54:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0020.hostedemail.com [216.40.44.20]) by kanga.kvack.org (Postfix) with ESMTP id 005D08E0003 for ; Wed, 22 Apr 2020 08:54:29 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id A69572DFD for ; Wed, 22 Apr 2020 12:54:29 +0000 (UTC) X-FDA: 76735484658.11.boys92_a0e8e37b725e X-HE-Tag: boys92_a0e8e37b725e X-Filterd-Recvd-Size: 7186 Received: from mail-qk1-f196.google.com (mail-qk1-f196.google.com [209.85.222.196]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Wed, 22 Apr 2020 12:54:28 +0000 (UTC) Received: by mail-qk1-f196.google.com with SMTP id b188so575247qkd.9 for ; Wed, 22 Apr 2020 05:54:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=egNubIbVKUeiZiZM/7yehbT1ogKxBreptaP/+smyZZg=; b=f7lwEsYnoj7CxiAJlGIx77t8XjowVlUeeL7UpgKiZ7XL52S9gvOFgpTNpq0cPXJHQ0 kOA85dlDnIBBaXSE8nQC2DIbzl0yYCFEh4wHy8XU0LrTrfSlxQd0FIsI7GxrfQ0TvV8k +EphoF7BWZnPkhkkPzZTPpsZxFJtaxNVWopR95sxZj47pxeij7FblSKLlF/Qk4DNHMio /p+bYUa2TwPxPeO6WhNvDNcFqjGg8IfN90dUcVMTybUEoY5uab/S3DXyr4MJugRd9Ruv UTx4M/mhMKcU91YzOD29WyPPjpQeDS3Xw5qjKnWWgNv+9Afp+M6DZnjVKZ2+tlkuonKb 0V8g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=egNubIbVKUeiZiZM/7yehbT1ogKxBreptaP/+smyZZg=; b=XU2yPRFJl8rDY6o3tNAqMsIA3zbMzhyrmbbJRa4+KAnvLu5a+iIQ2/3VgvsPJow50C Ak/fAsrIrSSrBIgPPEQ+S6EDXxiM8+XMtlYhNvIlGid11FwhozFOYSpnKKr4Xi8zAeM/ VcZaJXAXF1rav+5MiMHQysB0yN8/pVl6/p92fsldGFMh4E9C/dv0OOkP5nztB0h/ptys 9Oa6OwCWPUHss1ny0U2U8+B0TGah3G5d3dqGY9BFR1CpEFsxWDAWqdn6v8RVcldI+P1Y o/OWBjhlu7B4gwjNSoENJRzI55s+qX5BNF5J5BwqsW/4XSOsUe6ryaukLzNOgSvBtAl8 hb2w== X-Gm-Message-State: AGi0PuZ98Kz1qoiRStas8xL2fbeZUZbYuesRQIbNh8U0Q0LB71YGELKt Tus7k2m7Il3o34IWH+r2xxUTVg== X-Google-Smtp-Source: APiQypKuwEh+QBwJzUyuvXuzFhjkxWupX50kjx/Pf6mFO+EkK8hDeHzVy6DEuyJzITBXmQ60gSycbQ== X-Received: by 2002:a37:a650:: with SMTP id p77mr24971429qke.342.1587560068305; Wed, 22 Apr 2020 05:54:28 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::921]) by smtp.gmail.com with ESMTPSA id z4sm2721634qtq.5.2020.04.22.05.54.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Apr 2020 05:54:27 -0700 (PDT) Date: Wed, 22 Apr 2020 08:54:26 -0400 From: Johannes Weiner To: Yafang Shao Cc: akpm@linux-foundation.org, mhocko@kernel.org, linux-mm@kvack.org, Chris Down , Shakeel Butt Subject: Re: [PATCH v2] mm, memcg: fix inconsistent oom event behavior Message-ID: <20200422125426.GC358439@cmpxchg.org> References: <20200422110643.15725-1-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200422110643.15725-1-laoar.shao@gmail.com> 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 Wed, Apr 22, 2020 at 07:06:43AM -0400, Yafang Shao wrote: > A recent commit 9852ae3fe529 ("mm, memcg: consider subtrees in > memory.events") changes the behavior of memcg events, which will > consider subtrees in memory.events. But oom_kill event is a special one > as it is used in both cgroup1 and cgroup2. In cgroup1, it is displayed > in memory.oom_control. The file memory.oom_control is in both root memcg > and non root memcg, that is different with memory.event as it only in > non-root memcg. That commit is okay for cgroup2, but it is not okay for > cgroup1 as it will cause inconsistent behavior between root memcg and > non-root memcg. > > Here's an example on why this behavior is inconsistent in cgroup1. > root memcg > / > memcg foo > / > memcg bar > > Suppose there's an oom_kill in memcg bar, then the oon_kill will be > > root memcg : memory.oom_control(oom_kill) 0 > / > memcg foo : memory.oom_control(oom_kill) 1 > / > memcg bar : memory.oom_control(oom_kill) 1 > > For the non-root memcg, its memory.oom_control(oom_kill) includes its > descendants' oom_kill, but for root memcg, it doesn't include its > descendants' oom_kill. That means, memory.oom_control(oom_kill) has > different meanings in different memcgs. That is inconsistent. Then the user > has to know whether the memcg is root or not. > > If we can't fully support it in cgroup1, for example by adding > memory.events.local into cgroup1 as well, then let's don't touch > its original behavior. > > Setting CGRP_ROOT_MEMORY_LOCAL_EVENTS for legacy hierarchy by > default rather than special casing it somewhere quite deep in the code > would be better, per discussion with Michal. > > Fixes: 9852ae3fe529 ("mm, memcg: consider subtrees in memory.events") > Cc: Chris Down > Cc: Shakeel Butt > Cc: Michal Hocko > Cc: Johannes Weiner > Signed-off-by: Yafang Shao > --- > mm/memcontrol.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 5beea03dd58a..0f7381bddcee 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5940,10 +5940,20 @@ static void mem_cgroup_bind(struct cgroup_subsys_state *root_css) > * guarantees that @root doesn't have any children, so turning it > * on for the root memcg is enough. > */ > - if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) > + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) { > root_mem_cgroup->use_hierarchy = true; > - else > + } else { > root_mem_cgroup->use_hierarchy = false; > + /* > + * Set CGRP_ROOT_MEMORY_LOCAL_EVENTS for legacy hierarchy > + * by default to avoid inconsistent oom_kill behavior > + * between root memcg and non-root memcg. > + * Regarding default hierarchy, as this flag will be set > + * or cleared later, we don't need to process it in this > + * function. > + */ > + cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS; That will cause problems for people trying to remount. From cgroup1_reconfigure(): /* Don't allow flags or name to change at remount */ if ((ctx->flags ^ root->flags) || (ctx->name && strcmp(ctx->name, root->name))) { errorfc(fc, "option or name mismatch, new: 0x%x \"%s\", old: 0x%x \"%s\"", ctx->flags, ctx->name ?: "", root->flags, root->name); ret = -EINVAL; goto out_unlock; } These flags belong to the user, they're read-only to the cgroup implementation. Let's not mess with them from a controller. diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 4b868e5a687f..e831a90b5506 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -773,6 +773,8 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg, atomic_long_inc(&memcg->memory_events[event]); cgroup_file_notify(&memcg->events_file); + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) + break; if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS) break; } while ((memcg = parent_mem_cgroup(memcg)) &&