linux-kernel - Re: [PATCH] mm: memcontrol: fix NR_WRITEBACK leak in memcg and system stats

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Message-ID: <CALvZod5-35Y+_eot6-6J5HyssnmAW-wfYhuQdxxA9Zj8Ng2e+g@mail.gmail.com>
Date:   Wed, 7 Feb 2018 07:44:08 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@...com
Subject: Re: [PATCH] mm: memcontrol: fix NR_WRITEBACK leak in memcg and system stats

On Sat, Feb 3, 2018 at 12:23 AM, Johannes Weiner <hannes@...xchg.org> wrote:
> After the ("a983b5ebee57 mm: memcontrol: fix excessive complexity in
> memory.stat reporting"), we observed slowly upward creeping
> NR_WRITEBACK counts over the course of several days, both the
> per-memcg stats as well as the system counter in e.g. /proc/meminfo.
>
> The conversion from full per-cpu stat counts to per-cpu cached atomic
> stat counts introduced an irq-unsafe RMW operation into the updates.
>
> Most stat updates come from process context, but one notable exception
> is the NR_WRITEBACK counter. While writebacks are issued from process
> context, they are retired from (soft)irq context.
>
> When writeback completions interrupt the RMW counter updates of new
> writebacks being issued, the decs from the completions are lost.
>
> Since the global updates are routed through the joint lruvec API, both
> the memcg counters as well as the system counters are affected.
>
> This patch makes the joint stat and event API irq safe.
>
> Fixes: a983b5ebee57 ("mm: memcontrol: fix excessive complexity in memory.stat reporting")
> Debugged-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Should this be considered for stable?