Re: [PATCH] memcg: schedule high reclaim for remote memcgs on high_work

[Shakeel Butt <shakeelb@google.com>]

On Tue, Jan 8, 2019 at 6:59 AM Michal Hocko <mhocko@kernel.org> wrote:
>
> On Wed 02-01-19 17:56:38, Shakeel Butt wrote:
> > If a memcg is over high limit, memory reclaim is scheduled to run on
> > return-to-userland. However it is assumed that the memcg is the current
> > process's memcg. With remote memcg charging for kmem or swapping in a
> > page charged to remote memcg, current process can trigger reclaim on
> > remote memcg. So, schduling reclaim on return-to-userland for remote
> > memcgs will ignore the high reclaim altogether. So, punt the high
> > reclaim of remote memcgs to high_work.
>
> Have you seen this happening in real life workloads?

No, just during code review.

> And is this offloading what we really want to do?

That's the question I am brainstorming nowadays. More generally how
memcg-oom-kill should work in the remote memcg charging case.

> I mean it is clearly the current
> task that has triggered the remote charge so why should we offload that
> work to a system? Is there any reason we cannot reclaim on the remote
> memcg from the return-to-userland path?
>

The only reason I did this was the code was much simpler but I see
that the current is charging the given memcg and maybe even
reclaiming, so, why not do the high reclaim as well. I will update the
patch.

thanks,
Shakeel