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

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Message-ID: <e0812074-0b4f-bba1-ccea-a82c9312da44@alibaba-inc.com>
Date:   Mon, 02 Oct 2017 23:44:55 +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 2/3] mm: oom: show unreclaimable slab info when kernel
 panic



On 10/2/17 12:26 AM, Michal Hocko wrote:
> 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.

It has been removed since v8. Currently the only condition is 
unreclaimable slabs > user memory.

Thanks,
Yang

>