Re: [PATCH v3 1/4] memcg: introduce per-memcg reclaim interface

[Yosry Ahmed]

On Fri, Apr 8, 2022 at 7:55 AM Dan Schatzberg <schatzberg.dan@xxxxxxxxx> wrote:
>
> On Fri, Apr 08, 2022 at 04:11:05PM +0200, Michal Hocko wrote:
> > Regarding "max" as a possible input. I am not really sure to be honest.
> > I can imagine that it could be legit to simply reclaim all the charges
> > (e.g. before removing the memcg) which should be achieveable by
> > reclaiming the reported consumption. Or what exactly should be the
> > semantic?
>
> Yeah, it just allows you to avoid reading memory.current to just
> reclaim everything if you can specify "max" - you're still protected
> by nretries to eventually bail out. Mostly, though I just feel like
> supporting "max" makes memory.reclaim semetric with a lot of the
> cgroup memory control files which tend to support "max".

One possible approach here is to have force_empty behavior when we
write "max" to memory.reclaim. From Google's perspective we don't have
a preference, but it seems to me like logical behavior. We can do this
either by directly calling mem_cgroup_force_empty() or just draining
stock and lrus in memory_reclaim().

This actually brings up another interesting point. Do you think we
should drain lrus if try_to_free_mem_cgroup_pages() fails to reclaim
the request amount? We can do this after the first call or before the
last one. It could introduce more evictable pages for
try_to_free_mem_cgroup_pages() to free.