linux-kernel - Re: [Resend PATCH 2/6] mm/memcg: remove useless check on page->mem

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Message-ID: <20200813110102.GF9477@dhcp22.suse.cz>
Date:   Thu, 13 Aug 2020 13:01:02 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Resend PATCH 2/6] mm/memcg: remove useless check on
 page->mem_cgroup

On Thu 13-08-20 17:45:19, Alex Shi wrote:
> 
> 
> 在 2020/8/13 下午2:20, Michal Hocko 写道:
> > On Wed 12-08-20 11:25:53, Alex Shi wrote:
> >> >From 999b0fe5fc65865c3b59ff28500d45572a4a9570 Mon Sep 17 00:00:00 2001
> >> From: Alex Shi <alex.shi@...ux.alibaba.com>
> >> Date: Wed, 5 Aug 2020 21:02:30 +0800
> >> Subject: [PATCH 2/6] mm/memcg: bail out early from swap accounting when memcg
> >>  is disabled
> >>
> >> If we disabled memcg by cgroup_disable=memory, page->memcg will be NULL
> >> and so the charge is skipped and that will trigger a warning like below.
> >> Let's return from the funcs earlier.
> >>
> >>  ---[ end trace f1f34bfc3b32ed2f ]---
> >>  anon flags:0x5005b48008000d(locked|uptodate|dirty|swapbacked)
> >>  raw: 005005b48008000d dead000000000100 dead000000000122 ffff8897c7c76ad1
> >>  raw: 0000000000000022 0000000000000000 0000000200000000 0000000000000000
> >>  page dumped because: VM_WARN_ON_ONCE_PAGE(!memcg)
> > 
> > Yes this is better. It would be even more informative if you added the
> > backtrace.
> 
> The stack is a bit long.

This doesn't matter. It is informative and potentially useful for future
reference.

Thanks!
-- 
Michal Hocko
SUSE Labs