linux-kernel - Re: [PATCH v2 2/2] memcg: dump memory.stat during cgroup OOM for v1

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Date:   Wed, 3 May 2023 18:04:29 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>, Chris Li <chrisl@...nel.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] memcg: dump memory.stat during cgroup OOM for v1

On Fri, Apr 28, 2023 at 01:24:06PM +0000, Yosry Ahmed wrote:
> Commit c8713d0b2312 ("mm: memcontrol: dump memory.stat during cgroup
> OOM") made sure we dump all the stats in memory.stat during a cgroup
> OOM, but it also introduced a slight behavioral change. The code used to
> print the non-hierarchical v1 cgroup stats for the entire cgroup
> subtree, now it only prints the v2 cgroup stats for the cgroup under
> OOM.
> 
> For cgroup v1 users, this introduces a few problems:
> (a) The non-hierarchical stats of the memcg under OOM are no longer
> shown.
> (b) A couple of v1-only stats (e.g. pgpgin, pgpgout) are no longer
> shown.
> (c) We show the list of cgroup v2 stats, even in cgroup v1. This list of
> stats is not tracked with v1 in mind. While most of the stats seem to be
> working on v1, there may be some stats that are not fully or correctly
> tracked.
> 
> Although OOM log is not set in stone, we should not change it for no
> reason. When upgrading the kernel version to a version including
> commit c8713d0b2312 ("mm: memcontrol: dump memory.stat during cgroup
> OOM"), these behavioral changes are noticed in cgroup v1.
> 
> The fix is simple. Commit c8713d0b2312 ("mm: memcontrol: dump memory.stat
> during cgroup OOM") separated stats formatting from stats display for
> v2, to reuse the stats formatting in the OOM logs. Do the same for v1.
> 
> Move the v2 specific formatting from memory_stat_format() to
> memcg_stat_format(), add memcg1_stat_format() for v1, and make
> memory_stat_format() select between them based on cgroup version.
> Since memory_stat_show() now works for both v1 & v2, drop
> memcg_stat_show().
> 
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

Acked-by: Shakeel Butt <shakeelb@...gle.com>