Re: [RFC] Per file OOM badness

[Nicolai HÃhnle]

On 30.01.2018 11:48, Michel DÃnzer wrote:
> On 2018-01-30 11:42 AM, Daniel Vetter wrote:
> > On Tue, Jan 30, 2018 at 10:43:10AM +0100, Michel DÃnzer wrote:
> > > On 2018-01-30 10:31 AM, Daniel Vetter wrote:
> > >
> > > > I guess a good first order approximation would be if we simply charge any
> > > > newly allocated buffers to the process that created them, but that means
> > > > hanging onto lots of mm_struct pointers since we want to make sure we then
> > > > release those pages to the right mm again (since the process that drops
> > > > the last ref might be a totally different one, depending upon how the
> > > > buffers or DRM fd have been shared).
> > > >
> > > > 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.
> >
> > I'm not concerned about wrongly accounting shared buffers (they don't
> > matter), but imbalanced accounting. I.e. allocate a buffer in the client,
> > share it, but then the compositor drops the last reference.
>
> I don't think the order matters. The memory is "uncharged" in each
> process when it drops its reference.

Daniel made a fair point about passing DRM fds between processes, though.

It's not a problem with how the fds are currently used, but somebody 
could do the following:

1. Create a DRM fd in process A, allocate lots of buffers.
2. Pass the fd to process B via some IPC mechanism.
3. Exit process A.

There needs to be some assurance that the BOs are accounted as belonging 
to process B in the end.

Cheers,
Nicolai
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