linux-kernel - Re: [PATCH 2/3] mm: oom: show unreclaimable slab info when kernel panic

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Date:   Mon, 2 Oct 2017 09:26:07 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Yang Shi <yang.s@...baba-inc.com>
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm: oom: show unreclaimable slab info when kernel
 panic

On Thu 28-09-17 01:25:50, Yang Shi wrote:
> 
> 
> On 9/27/17 3:45 AM, Michal Hocko wrote:
> > On Wed 27-09-17 08:53:35, Yang Shi wrote:
> > > Kernel may panic when oom happens without killable process sometimes it
> > > is caused by huge unreclaimable slabs used by kernel.
> > > 
> > > Although kdump could help debug such problem, however, kdump is not
> > > available on all architectures and it might be malfunction sometime.
> > > And, since kernel already panic it is worthy capturing such information
> > > in dmesg to aid touble shooting.
> > > 
> > > Print out unreclaimable slab info (used size and total size) which
> > > actual memory usage is not zero (num_objs * size != 0) when:
> > >    - unreclaimable slabs : all user memory > unreclaim_slabs_oom_ratio
> > >    - panic_on_oom is set or no killable process
> > 
> > OK, this is better but I do not see why this should be tunable via proc.
> 
> Just thought someone might want to dump unreclaimable slab info
> unconditionally.

If that ever happens then we will eventually add it. But do not add proc
knobs for theoretical usecases. We will have to maintain them and it
can turn into a maint. pain. Like some others in the past.
-- 
Michal Hocko
SUSE Labs