linux-kernel - Re: WARNINGs in set_task_reclaim_state with memory cgroup and full memory usage

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Message-ID: <20190827115014.GZ7538@dhcp22.suse.cz>
Date:   Tue, 27 Aug 2019 13:50:14 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>,
        Adric Blake <promarbler14@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: WARNINGs in set_task_reclaim_state with memory cgroup and full
 memory usage

On Tue 27-08-19 19:43:49, Yafang Shao wrote:
> On Tue, Aug 27, 2019 at 6:43 PM Michal Hocko <mhocko@...nel.org> wrote:
> >
> > If there are no objection to the patch I will post it as a standalong
> > one.
> 
> I have no objection to your patch. It could fix the issue.
> 
> I still think that it is not proper to use a new scan_control here as
> it breaks the global reclaim context.
>
> This context switch from global reclaim to memcg reclaim is very
> subtle change to the subsequent processing, that may cause some
> unexpected behavior.

Why would it break it? Could you be more specific please?

> Anyway, we can send this patch as a standalong one.
> Feel free to add:
> 
> Acked-by: Yafang Shao <laoar.shao@...il.com>

Thanks!
-- 
Michal Hocko
SUSE Labs