linux-kernel - Re: [PATCH 03/13] mm: shmem: provide oom badness for shmem files

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Message-ID: <081e264f-c60c-4d25-e5bb-3f135f5eb270@amd.com>
Date:   Mon, 13 Jun 2022 11:11:31 +0200
From:   Christian König <christian.koenig@....com>
To:     Michel Dänzer <michel.daenzer@...lbox.org>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Michal Hocko <mhocko@...e.com>
Cc:     andrey.grodzovsky@....com, linux-mm@...ck.org,
        nouveau@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        hughd@...gle.com, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, linux-fsdevel@...r.kernel.org,
        viro@...iv.linux.org.uk, daniel@...ll.ch,
        linux-tegra@...r.kernel.org, alexander.deucher@....com,
        akpm@...ux-foundation.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 03/13] mm: shmem: provide oom badness for shmem files

Am 13.06.22 um 11:08 schrieb Michel Dänzer:
> On 2022-06-11 10:06, Christian König wrote:
>> Am 10.06.22 um 16:16 schrieb Michal Hocko:
>>> [...]
>>>>> Just consider the above mentioned memcg driven model. It doesn't really
>>>>> require to chase specific files and do some arbitrary math to share the
>>>>> responsibility. It has a clear accounting and responsibility model.
>>>> Ok, how does that work then?
>>> The memory is accounted to whoever faults that memory in or to the
>>> allocating context if that is a kernel memory (in most situations).
>> That's what I had in mind as well. Problem with this approach is that file descriptors are currently not informed that they are shared between processes.
>>
>> So to make this work we would need something like attach/detach to process in struct file_operations.
>>
>> And as I noted, this happens rather often. For example a game which renders 120 frames per second needs to transfer 120 buffers per second between client and X.
> FWIW, in the steady state, the game will cycle between a small (generally 2-5) set of buffers. The game will not cause new buffers to be exported & imported for every frame.
>
> In general, I'd expect dma-buf export & import to happen relatively rarely, e.g. when a window is opened or resized.

Yeah, on a normal Linux desktop. Just unfortunately not on Android :)

Anyway even when this only happens on game start we can't go over all 
the processes/fds and check where a DMA-buf is opened to account this 
against each process.

We would need to add callbacks for this to make it work halve way reliable.

Christian.