Re: [PATCH] procfs/dmabuf: Add /proc//task//dmabuf_fds

Michal Hocko
2021-01-27T11:27:37Z

On Wed 27-01-21 12:08:50, Christian König wrote:
> Am 27.01.21 um 12:02 schrieb Michal Hocko:
> > On Wed 27-01-21 11:53:55, Christian König wrote:
> > [...]
> > > In general processes are currently not held accountable for memory they
> > > reference through their file descriptors. DMA-buf is just one special case.
> > True
> >
> > > In other words you can currently do something like this
> > >
> > > fd = memfd_create("test", 0);
> > > while (1)
> > >     write(fd, buf, 1024);
> > >
> > > and the OOM killer will terminate random processes, but never the one
> > > holding the memfd reference.
> > memfd is just shmem under cover, no? And that means that the memory gets
> > accounted to MM_SHMEMPAGES. But you are right that this in its own
> > doesn't help much if the fd is shared and the memory stays behind a
> > killed victim.
>
> I think so, yes. But I just tested this and it doesn't seem to work
> correctly.
>
> When I run the few lines above the OOM killer starts to terminate processes,
> but since my small test program uses very very little memory basically
> everything else gets terminated (including X, desktop, sshd etc..) before it
> is terminated as well.

Something worth looking into. Maybe those pages are not really accounted
properly after all. Can you send a separate email about details with oom
reports please?
--
Michal Hocko
SUSE Labs