linux-kernel - Re: [PATCH 0/2 v4] oom: capture unreclaimable slab info in oom message when kernel panic

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Date:   Mon, 25 Sep 2017 23:55:19 +0800
From:   "Yang Shi" <yang.s@...baba-inc.com>
To:     Michal Hocko <mhocko@...nel.org>
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 0/2 v4] oom: capture unreclaimable slab info in oom
 message when kernel panic



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

>