linux-kernel - Re: [PATCH] mm/memcg: remove useless check on page->mem

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Message-ID: <20200810095310.GD4773@dhcp22.suse.cz>
Date:   Mon, 10 Aug 2020 11:53:10 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/memcg: remove useless check on page->mem_cgroup

On Mon 10-08-20 11:52:02, Michal Hocko wrote:
> On Wed 05-08-20 21:02:30, Alex Shi wrote:
> > 
> > 
> > 在 2020/8/5 下午8:28, Alex Shi 写道:
> > > The last patch has a problem on define. this version could fix it.
> > > 
> > > BTW, I see some !memcg happens when MEMCG compilered but disabled by cgroup_disable
> > > 
> > > 
> > > [   94.657666] ---[ end trace f1f34bfc3b32ed2f ]---
> > > [   95.138995] anon flags: 0x5005b48008000d(locked|uptodate|dirty|swapbacked)
> > > [   95.146220] raw: 005005b48008000d dead000000000100 dead000000000122 ffff8897c7c76ad1
> > > [   95.154549] raw: 0000000000000022 0000000000000000 0000000200000000 0000000000000000
> > > [   95.162876] page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg)
> > > 
> > > 
> > 
> > The following patch may helpful.
> > 
> > >From 8bfb26a2e37e08dc61d20212bcfa5812a367ba94 Mon Sep 17 00:00:00 2001
> > From: Alex Shi <alex.shi@...ux.alibaba.com>
> > Date: Wed, 5 Aug 2020 20:32:12 +0800
> > Subject: [PATCH] mm/memcg: don't try charge swap if memcg disabled
> > 
> > If we disabled memcg by cgroup_disable=memory, the swap charges are
> > still called. Let's return from the funcs earlier and keep WARN_ON
> > monitor.
> 
> Do I get it right that this is on top of your patch to remove the memcg
> check or a preparatory work?

Sorry meant to say - add the warning rather than drop the check.

> Both are good but it would be better to
> call that out specifically for clarity (along with the warning if that
> is a follow up fix).
-- 
Michal Hocko
SUSE Labs