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Subject: Re: [PATCH 0/2 v4] oom: capture unreclaimable slab info in oom
 message when kernel panic
References: <1505947132-4363-1-git-send-email-yang.s@alibaba-inc.com>
 <20170925142352.havlx6ikheanqyhj@dhcp22.suse.cz>
From: "Yang Shi" <yang.s@alibaba-inc.com>
Message-ID: <e773cd57-8df6-ee6e-d051-857b8f354a0a@alibaba-inc.com>
Date: Mon, 25 Sep 2017 23:55:19 +0800
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To: Michal Hocko <mhocko@kernel.org>
Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org



On 9/25/17 7:23 AM, Michal Hocko wrote:
> On Thu 21-09-17 06:38:50, Yang Shi wrote:
>> Recently we ran into a oom issue, kernel panic due to no killable process.
>> The dmesg shows huge unreclaimable slabs used almost 100% memory, but kdump doesn't capture vmcore due to some reason.
>>
>> So, it may sound better to capture unreclaimable slab info in oom message when kernel panic to aid trouble shooting and cover the corner case.
>> Since kernel already panic, so capturing more information sounds worthy and doesn't bother normal oom killer.
>>
>> With the patchset, tools/vm/slabinfo has a new option, "-U", to show unreclaimable slab only.
>>
>> And, oom will print all non zero (num_objs * size != 0) unreclaimable slabs in oom killer message.
> 
> Well, I do undestand that this _might_ be useful but it also might
> generates a _lot_ of output. The oom report can be quite verbose already
> so is this something we want to have enabled by default?

The uneclaimable slub message will be just printed out when kernel panic 
(no killable process or panic_on_oom is set). So, it will not bother 
normal oom. Since kernel is already panic, so it might be preferred to 
have more information reported.

We definitely can add a proc knob to control it if we want to disable 
the message even if when kernel panic.

Thanks,
Yang

> 

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