linux-kernel - Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

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Date:   Tue, 20 Apr 2021 09:47:43 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Christian König <christian.koenig@....com>,
        Peter.Enderborg@...y.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, sumit.semwal@...aro.org,
        adobriyan@...il.com, akpm@...ux-foundation.org,
        songmuchun@...edance.com, guro@...com, shakeelb@...gle.com,
        neilb@...e.de, samitolvanen@...gle.com,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, willy@...radead.org
Subject: Re: [PATCH v4] dma-buf: Add DmaBufTotal counter in meminfo

On Tue 20-04-21 10:20:43, Mike Rapoport wrote:
> On Tue, Apr 20, 2021 at 09:04:51AM +0200, Michal Hocko wrote:
> > On Mon 19-04-21 18:37:13, Christian König 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?

Not sure which specific parts (likely the unaccounted memory?) but sure
why not. Our /proc/meminfo is rather underdocumented. More information
cannot hurt.
-- 
Michal Hocko
SUSE Labs