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

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Message-ID: <dce6d244-36c7-7452-97f5-7437bd78cfcc@gmail.com>
Date:   Tue, 30 Jan 2018 12:28:37 +0100
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Michel Dänzer <michel@...nzer.net>,
        Christian König <christian.koenig@....com>,
        Michal Hocko <mhocko@...nel.org>, Roman Gushchin <guro@...com>
Cc:     linux-mm@...ck.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [RFC] Per file OOM badness

Am 30.01.2018 um 12:02 schrieb Michel Dänzer:
> On 2018-01-30 11:40 AM, Christian König wrote:
>> Am 30.01.2018 um 10:43 schrieb Michel Dänzer:
>>> [SNIP]
>>>> Would it be ok to hang onto potentially arbitrary mmget references
>>>> essentially forever? If that's ok I think we can do your process based
>>>> account (minus a few minor inaccuracies for shared stuff perhaps, but no
>>>> one cares about that).
>>> Honestly, I think you and Christian are overthinking this. Let's try
>>> charging the memory to every process which shares a buffer, and go from
>>> there.
>> My problem is that this needs to be bullet prove.
>>
>> For example imagine an application which allocates a lot of BOs, then
>> calls fork() and let the parent process die. The file descriptor lives
>> on in the child process, but the memory is not accounted against the child.
> What exactly are you referring to by "the file descriptor" here?

The file descriptor used to identify the connection to the driver. In 
other words our drm_file structure in the kernel.

> What happens to BO handles in general in this case? If both parent and
> child process keep the same handle for the same BO, one of them
> destroying the handle will result in the other one not being able to use
> it anymore either, won't it?
Correct.

That usage is actually not useful at all, but we already had 
applications which did exactly that by accident.

Not to mention that somebody could do it on purpose.

Regards,
Christian.