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

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Message-ID: <20170927104537.r42javxhnyqlxnqm@dhcp22.suse.cz>
Date:   Wed, 27 Sep 2017 12:45:37 +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 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.
Can we start with simple NR_SLAB_UNRECLAIMABLE > LRU_PAGES and place it
into dump_header so that we get the report also during regular OOM?
-- 
Michal Hocko
SUSE Labs