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Date:   Wed, 20 Oct 2021 10:55:27 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Zhaoyang Huang <huangzhaoyang@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: skip current when memcg reclaim
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On Wed 20-10-21 15:33:39, Zhaoyang Huang wrote:
[...]
> Do you mean that direct reclaim should succeed for the first round
> reclaim within which memcg get protected by memory.low and would NOT
> retry by setting memcg_low_reclaim to true?

Yes, this is the semantic of low limit protection in the upstream
kernel. Have a look at do_try_to_free_pages and how it sets
memcg_low_reclaim only if there were no pages reclaimed.

> It is not true in android
> like system, where reclaim always failed and introduce lmk and even
> OOM.

I am not familiar with android specific changes to the upstream reclaim
logic. You should be investigating why the reclaim couldn't make a
forward progress (aka reclaim pages) from non-protected memcgs. There
are tracepoints you can use (generally vmscan prefix).

-- 
Michal Hocko
SUSE Labs