Re: [RFC] Per file OOM badness

[Michal Hocko <mhocko@kernel.org>]

On Tue 23-01-18 17:39:19, Michel Danzer wrote:
> On 2018-01-23 04:36 PM, Michal Hocko wrote:
> > On Tue 23-01-18 15:27:00, Roman Gushchin wrote:
> >> On Thu, Jan 18, 2018 at 06:00:06PM +0100, Michal Hocko wrote:
> >>> On Thu 18-01-18 11:47:48, Andrey Grodzovsky wrote:
> >>>> Hi, this series is a revised version of an RFC sent by Christian Konig
> >>>> a few years ago. The original RFC can be found at 
> >>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.freedesktop.org_archives_dri-2Ddevel_2015-2DSeptember_089778.html&d=DwIDAw&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=R-JIQjy8rqmH5qD581_VYL0Q7cpWSITKOnBCE-3LI8U&s=QZGqKpKuJ2BtioFGSy8_721owcWJ0J6c6d4jywOwN4w&
> >>> Here is the origin cover letter text
> >>> : I'm currently working on the issue that when device drivers allocate memory on
> >>> : behalf of an application the OOM killer usually doesn't knew about that unless
> >>> : the application also get this memory mapped into their address space.
> >>> : 
> >>> : This is especially annoying for graphics drivers where a lot of the VRAM
> >>> : usually isn't CPU accessible and so doesn't make sense to map into the
> >>> : address space of the process using it.
> >>> : 
> >>> : The problem now is that when an application starts to use a lot of VRAM those
> >>> : buffers objects sooner or later get swapped out to system memory, but when we
> >>> : now run into an out of memory situation the OOM killer obviously doesn't knew
> >>> : anything about that memory and so usually kills the wrong process.
> >>> : 
> >>> : The following set of patches tries to address this problem by introducing a per
> >>> : file OOM badness score, which device drivers can use to give the OOM killer a
> >>> : hint how many resources are bound to a file descriptor so that it can make
> >>> : better decisions which process to kill.
> >>> : 
> >>> : So question at every one: What do you think about this approach?
> >>> : 
> >>> : My biggest concern right now is the patches are messing with a core kernel
> >>> : structure (adding a field to struct file). Any better idea? I'm considering
> >>> : to put a callback into file_ops instead.
> >>
> >> Hello!
> >>
> >> I wonder if groupoom (aka cgroup-aware OOM killer) can work for you?
> > 
> > I do not think so. The problem is that the allocating context is not
> > identical with the end consumer.
> 
> That's actually not really true. Even in cases where a BO is shared with
> a different process, it is still used at least occasionally in the
> process which allocated it as well. Otherwise there would be no point in
> sharing it between processes.

OK, but somebody has to be made responsible. Otherwise you are just
killing a process which doesn't really release any memory.
 
> There should be no problem if the memory of a shared BO is accounted for
> in each process sharing it. It might be nice to scale each process'
> "debt" by 1 / (number of processes sharing it) if possible, but in the
> worst case accounting it fully in each process should be fine.

So how exactly then helps to kill one of those processes? The memory
stays pinned behind or do I still misunderstand?
-- 
Michal Hocko
SUSE Labs

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