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Date:   Tue, 20 Apr 2021 10:20:43 +0300
From:   Mike Rapoport <rppt@kernel.org>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Christian =?iso-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>,
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Subject: Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo
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On Tue, Apr 20, 2021 at 09:04:51AM +0200, Michal Hocko wrote:
> On Mon 19-04-21 18:37:13, Christian K?nig wrote:
> > Am 19.04.21 um 18:11 schrieb Michal Hocko:
> [...]
> > > The question is not whether it is NUMA aware but whether it is useful to
> > > know per-numa data for the purpose the counter is supposed to serve.
> > 
> > No, not at all. The pages of a single DMA-buf could even be from different
> > NUMA nodes if the exporting driver decides that this is somehow useful.
> 
> As the use of the counter hasn't been explained yet I can only
> speculate. One thing that I can imagine to be useful is to fill gaps in
> our accounting. It is quite often that the memroy accounted in
> /proc/meminfo (or oom report) doesn't add up to the overall memory
> usage. In some workloads the workload can be huge! In many cases there
> are other means to find out additional memory by a subsystem specific
> interfaces (e.g. networking buffers). I do assume that dma-buf is just
> one of those and the counter can fill the said gap at least partially
> for some workloads. That is definitely useful.

A bit off-topic.

Michal, I think it would have been nice to have an explanation like above
in Documentation/proc/meminfo, what do you say?
 
> What I am trying to bring up with NUMA side is that the same problem can
> happen on per-node basis. Let's say that some user consumes unexpectedly
> large amount of dma-buf on a certain node. This can lead to observable
> performance impact on anybody on allocating from that node and even
> worse cause an OOM for node bound consumers. How do I find out that it
> was dma-buf that has caused the problem?
> 
> See where I am heading?

-- 
Sincerely yours,
Mike.