linux-kernel - Re: [RFC] Per file OOM badness

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Date:   Wed, 4 Apr 2018 11:09:25 +0200
From:   Michel Dänzer <michel@...nzer.net>
To:     Lucas Stach <l.stach@...gutronix.de>,
        Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Christian.Koenig@....com, linux-mm@...ck.org,
        amd-gfx@...ts.freedesktop.org, Roman Gushchin <guro@...com>
Subject: Re: [RFC] Per file OOM badness

On 2018-03-26 04:36 PM, Lucas Stach wrote:
> Am Dienstag, den 30.01.2018, 11:28 +0100 schrieb Michal Hocko:
>> On Tue 30-01-18 10:29:10, Michel Dänzer wrote:
>>> On 2018-01-24 12:50 PM, Michal Hocko wrote:
>>>> On Wed 24-01-18 12:23:10, Michel Dänzer wrote:
>>>>> On 2018-01-24 12:01 PM, Michal Hocko wrote:
>>>>>> On Wed 24-01-18 11:27:15, Michel Dänzer wrote:
>>>>
>>>> [...]
>>>>>>> 2. If the OOM killer kills a process which is sharing BOs
>>>>>>> with another
>>>>>>> process, this should result in the other process dropping
>>>>>>> its references
>>>>>>> to the BOs as well, at which point the memory is released.
>>>>>>
>>>>>> OK. How exactly are those BOs mapped to the userspace?
>>>>>
>>>>> I'm not sure what you're asking. Userspace mostly uses a GEM
>>>>> handle to
>>>>> refer to a BO. There can also be userspace CPU mappings of the
>>>>> BO's
>>>>> memory, but userspace doesn't need CPU mappings for all BOs and
>>>>> only
>>>>> creates them as needed.
>>>>
>>>> OK, I guess you have to bear with me some more. This whole stack
>>>> is a
>>>> complete uknonwn. I am mostly after finding a boundary where you
>>>> can
>>>> charge the allocated memory to the process so that the oom killer
>>>> can
>>>> consider it. Is there anything like that? Except for the proposed
>>>> file
>>>> handle hack?
>>>
>>> How about the other way around: what APIs can we use to charge /
>>> "uncharge" memory to a process? If we have those, we can experiment
>>> with
>>> different places to call them.
>>
>> add_mm_counter() and I would add a new counter e.g. MM_KERNEL_PAGES.
> 
> So is anyone still working on this? This is hurting us bad enough that
> I don't want to keep this topic rotting for another year.
> 
> If no one is currently working on this I would volunteer to give the
> simple "just account private, non-shared buffers in process RSS" a
> spin.

Sounds good. FWIW, I think shared buffers can also be easily handled by
accounting them in each process which has a reference. But that's more
of a detail, shouldn't make a big difference overall either way.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer