On 30.01.2018 11:48, Michel Dänzer wrote:
On 2018-01-30 11:42 AM, Daniel Vetter wrote:
On Tue, Jan 30, 2018 at 10:43:10AM +0100, Michel Dänzer 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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