linux-kernel - Re: [PATCH] procfs/dmabuf: Add /proc/<pid>/task/<tid>/dmabuf

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Date:   Wed, 27 Jan 2021 12:23:47 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Christian König <christian.koenig@....com>
Cc:     Kalesh Singh <kaleshsingh@...gle.com>, surenb@...gle.com,
        minchan@...nel.org, gregkh@...uxfoundation.org, hridya@...gle.com,
        jannh@...gle.com, kernel-team@...roid.com,
        Alexey Dobriyan <adobriyan@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Michel Lespinasse <walken@...gle.com>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Andrei Vagin <avagin@...il.com>,
        Yafang Shao <laoar.shao@...il.com>, Hui Su <sh_def@....com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] procfs/dmabuf: Add /proc/<pid>/task/<tid>/dmabuf_fds

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