linux-kernel - Re: [PATCH] memcg: schedule high reclaim for remote memcgs on high

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Date:   Tue, 8 Jan 2019 09:24:18 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: schedule high reclaim for remote memcgs on high_work

On Tue, Jan 8, 2019 at 6:59 AM Michal Hocko <mhocko@...nel.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