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

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Date:   Fri, 19 Jan 2018 17:54:36 +0100
From:   Christian König <christian.koenig@....com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Eric Anholt <eric@...olt.net>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org
Subject: Re: [RFC] Per file OOM badness

Am 19.01.2018 um 13:20 schrieb Michal Hocko:
> On Fri 19-01-18 13:13:51, Michal Hocko wrote:
>> On Fri 19-01-18 12:37:51, Christian König wrote:
>> [...]
>>> The per file descriptor badness is/was just the much easier approach to
>>> solve the issue, because the drivers already knew which client is currently
>>> using which buffer objects.
>>>
>>> I of course agree that file descriptors can be shared between processes and
>>> are by themselves not killable. But at least for our graphics driven use
>>> case I don't see much of a problem killing all processes when a file
>>> descriptor is used by more than one at the same time.
>> Ohh, I absolutely see why you have chosen this way for your particular
>> usecase. I am just arguing that this would rather be more generic to be
>> merged. If there is absolutely no other way around we can consider it
>> but right now I do not see that all other options have been considered
>> properly. Especially when the fd based approach is basically wrong for
>> almost anybody else.
> And more importantly. Iterating over _all_ fd which is what is your
> approach is based on AFAIU is not acceptable for the OOM path. Even
> though oom_badness is not a hot path we do not really want it to take a
> lot of time either. Even the current iteration over all processes is
> quite time consuming. Now you want to add the number of opened files and
> that might be quite many per process.

Mhm, crap that is a really good argument.

How about adding a linked list of callbacks to check for the OOM killer 
to check for each process?

This way we can avoid finding the process where we need to account 
things on when memory is allocated and still allow the OOM killer to 
only check the specific callbacks it needs to determine the score of a 
process?

Would still require some changes in the fs layer, but I think that 
should be doable.

Regards,
Christian.