linux-kernel - Re: [PATCH v1] mm:memcg: skip memcg of current in mem_cgroup_soft_limit

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Message-ID: <20180803061817.GC27245@dhcp22.suse.cz>
Date:   Fri, 3 Aug 2018 08:18:17 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        cgroups@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        kernel-patch-test@...ts.linaro.org
Subject: Re: [PATCH v1] mm:memcg: skip memcg of current in
 mem_cgroup_soft_limit_reclaim

On Fri 03-08-18 14:11:26, Zhaoyang Huang wrote:
> On Fri, Aug 3, 2018 at 1:48 PM Zhaoyang Huang <huangzhaoyang@...il.com> wrote:
> >
> > for the soft_limit reclaim has more directivity than global reclaim, we40960
> > have current memcg be skipped to avoid potential page thrashing.
> >
> The patch is tested in our android system with 2GB ram.  The case
> mainly focus on the smooth slide of pictures on a gallery, which used
> to stall on the direct reclaim for over several hundred
> millionseconds. By further debugging, we find that the direct reclaim
> spend most of time to reclaim pages on its own with softlimit set to
> 40960KB. I add a ftrace event to verify that the patch can help
> escaping such scenario. Furthermore, we also measured the major fault
> of this process(by dumpsys of android). The result is the patch can
> help to reduce 20% of the major fault during the test.

I have asked already asked. Why do you use the soft limit in the first
place? It is known to cause excessive reclaim and long stalls.
-- 
Michal Hocko
SUSE Labs