RE: [RFC] Per file OOM badness

[He, Roger]

-----Original Message-----
From: amd-gfx [mailto:amd-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Michal Hocko
Sent: Friday, January 19, 2018 1:14 AM
To: Grodzovsky, Andrey <Andrey.Grodzovsky@xxxxxxx>
Cc: linux-mm@xxxxxxxxx; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; Koenig, Christian <Christian.Koenig@xxxxxxx>
Subject: Re: [RFC] Per file OOM badness

On Thu 18-01-18 18:00:06, 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 
> > KÃnig a few years ago. The original RFC can be found at 
> > https://lists.freedesktop.org/archives/dri-devel/2015-September/0897
> > 78.html
> > 
> > This is the same idea and I've just adressed his concern from the 
> > original RFC and switched to a callback into file_ops instead of a new member in struct file.
> 
> Please add the full description to the cover letter and do not make 
> people hunt links.
> 
> 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.

	OK, but how do you attribute that memory to a particular OOM killable entity? And how do you actually enforce that those resources get freed on the oom killer action?

Here I think we need more fine granularity for distinguishing the buffer is taking VRAM or system memory.

> : 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.

But files are not killable, they can be shared... In other words this doesn't help the oom killer to make an educated guess at all.

> : 
> : So question at every one: What do you think about this approach?

	I thing is just just wrong semantically. Non-reclaimable memory is a pain, especially when there is way too much of it. If you can free that memory somehow then you can hook into slab shrinker API and react on the memory pressure. If you can account such a 	memory to a particular process and make sure that the consumption is bound by the process life time then we can think of an accounting that oom_badness can consider when selecting a victim.

I think you are misunderstanding here.
Actually for now, the memory in TTM Pools already has mm_shrink which is implemented in ttm_pool_mm_shrink_init.
And here the memory we want to make it contribute to OOM badness is not in TTM Pools.
Because when TTM buffer allocation success, the memory already is removed from TTM Pools.  

Thanks
Roger(Hongbo.He)

--
Michal Hocko
SUSE Labs
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