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

[Ganesan Rajagopal <rganesan@arista.com>]

On Fri, May 6, 2022 at 9:26 PM Shakeel Butt <shakeelb@google.com> wrote:
>
> On Fri, May 6, 2022 at 7:57 AM Johannes Weiner <hannes@cmpxchg.org> wrote:
> >
> > On Thu, May 05, 2022 at 05:13:30AM -0700, Ganesan Rajagopal wrote:
> > > v1 memcg exports memcg->watermark as "memory.mem_usage_in_bytes" in
> > > 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@arista.com>
> >
> > This wasn't initially added to cgroup2 because its usefulness is very
> > specific: it's (mostly) useless on limited cgroups, on long-running
> > cgroups, and on cgroups that are recycled for multiple jobs. And I
> > expect these categories apply to the majority of cgroup usecases.
> >
> > However, for the situation where you want to measure the footprint of
> > a short-lived, unlimited one-off cgroup, there really is no good
> > alternative. And it's a legitimate usecase. It doesn't cost much to
> > maintain this info. So I think we should go ahead with this patch.
> >
> > But please add a blurb to Documentation/admin-guide/cgroup-v2.rst.
>
> No objection from me. I do have two points: (1) watermark is not a
> good name for this interface, maybe max_usage or something. (2) a way
> to reset (i.e. write to it, reset it).

Thanks for the feedback. I'll post an updated patch with your suggestions
(including updating the description). For resetting the value I assume
setting it to memory.current would be logical?

Ganesan