Re: [PATCH] mm/memcontrol: Export memcg->watermark via sysfs for v2 memcg

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On Thu, May 5, 2022 at 10:27 AM Ganesan Rajagopal <rganesan@xxxxxxxxxx> wrote:
>
> On Thu, May 5, 2022 at 9:42 PM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> >
> > On Thu, May 5, 2022 at 5:13 AM Ganesan Rajagopal <rganesan@xxxxxxxxxx> wrote:
> > >
> > > v1 memcg exports memcg->watermark as "memory.mem_usage_in_bytes" in
> >
> > *max_usage_in_bytes
>
> Oops, thanks for the correction.
>
> > > sysfs. This is missing for v2 memcg though "memory.current" is exported.
> > > There is no other easy way of getting this information in Linux.
> > > getrsuage() returns ru_maxrss but that's the max RSS of a single process
> > > instead of the aggregated max RSS of all the processes. Hence, expose
> > > memcg->watermark as "memory.watermark" for v2 memcg.
> > >
> > > Signed-off-by: Ganesan Rajagopal <rganesan@xxxxxxxxxx>
> >
> > Can you please explain the use-case for which you need this metric?
> > Also note that this is not really an aggregated RSS of all the
> > processes in the cgroup. So, do you want max RSS or max charge and for
> > what use-case?
>
> We run a lot of automated tests when building our software and used to
> run into OOM scenarios when the tests run unbounded. We use this metric
> to heuristically limit how many tests can run in parallel using per test
> historical data.
>
> I understand this isn't really aggregated RSS, max charge works. We just
> need some metric to account for the peak memory usage.  We don't need
> it to be super accurate because there's significant variance between test
> runs anyway. We conservatively use the historical max to limit parallelism.
>
> Since this metric is not exposed in v2 memcg, the only alternative is to
> poll "memory.current" which would be quite inefficient and grossly
> inaccurate.
>

Oh also include the details you explained here in your commit message.



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