linux-kernel - Re: [PATCH] mm: memcg: Fix memcg reclaim soft lockup

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Message-ID: <20200826110015.GO22869@dhcp22.suse.cz>
Date:   Wed, 26 Aug 2020 13:00:15 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     xunlei <xlpang@...ux.alibaba.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: memcg: Fix memcg reclaim soft lockup

On Wed 26-08-20 18:41:18, xunlei wrote:
> On 2020/8/26 下午4:11, Michal Hocko wrote:
> > On Wed 26-08-20 15:27:02, Xunlei Pang wrote:
> >> We've met softlockup with "CONFIG_PREEMPT_NONE=y", when
> >> the target memcg doesn't have any reclaimable memory.
> > 
> > Do you have any scenario when this happens or is this some sort of a
> > test case?
> 
> It can happen on tiny guest scenarios.

OK, you made me more curious. If this is a tiny guest and this is a hard
limit reclaim path then we should trigger an oom killer which should
kill the offender and that in turn bail out from the try_charge lopp
(see should_force_charge). So how come this repeats enough in your setup
that it causes soft lockups?
-- 
Michal Hocko
SUSE Labs