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Date:   Tue, 29 Oct 2019 17:47:23 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Greg Thelen <gthelen@google.com>, Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzbot+13f93c99c06988391efe@syzkaller.appspotmail.com
Subject: Re: [PATCH] mm: vmscan: memcontrol: remove
 mem_cgroup_select_victim_node()
Message-Id: <20191029174723.ceb916ec850e7c88ed00e091@linux-foundation.org>
In-Reply-To: <20191029234753.224143-1-shakeelb@google.com>
References: <20191029234753.224143-1-shakeelb@google.com>
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On Tue, 29 Oct 2019 16:47:53 -0700 Shakeel Butt <shakeelb@google.com> wrote:

> Since commit 1ba6fc9af35b ("mm: vmscan: do not share cgroup iteration
> between reclaimers"), the memcg reclaim does not bail out earlier based
> on sc->nr_reclaimed and will traverse all the nodes. All the reclaimable
> pages of the memcg on all the nodes will be scanned relative to the
> reclaim priority. So, there is no need to maintain state regarding which
> node to start the memcg reclaim from. Also KCSAN complains data races in
> the code maintaining the state.
> 
> This patch effectively reverts the commit 889976dbcb12 ("memcg: reclaim
> memory from nodes in round-robin order") and the commit 453a9bf347f1
> ("memcg: fix numa scan information update to be triggered by memory
> event").
> 
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Reported-by: <syzbot+13f93c99c06988391efe@syzkaller.appspotmail.com>

The sysbot report
(http://lkml.kernel.org/r/00000000000055aba7058af4d378@google.com) was
for a null pointer deref.  So won't we be needing a Fixes: and cc:stable?