linux-kernel - Re: [RFC] mm: memcg: add priority for soft limit reclaiming

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Message-ID: <20190923132830.GQ6016@dhcp22.suse.cz>
Date:   Mon, 23 Sep 2019 15:28:30 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC] mm: memcg: add priority for soft limit reclaiming

On Mon 23-09-19 21:04:59, Hillf Danton wrote:
> 
> On Thu, 19 Sep 2019 21:32:31 +0800 Michal Hocko wrote:
> > 
> > On Thu 19-09-19 21:13:32, Hillf Danton wrote:
> > >
> > > Currently memory controler is playing increasingly important role in
> > > how memory is used and how pages are reclaimed on memory pressure.
> > >
> > > In daily works memcg is often created for critical tasks and their pre
> > > configured memory usage is supposed to be met even on memory pressure.
> > > Administrator wants to make it configurable that the pages consumed by
> > > memcg-B can be reclaimed by page allocations invoked not by memcg-A but
> > > by memcg-C.
> > 
> > I am not really sure I understand the usecase well but this sounds like
> > what memory reclaim protection in v2 is aiming at.
> > 

Please describe the usecase. 

> A tipoint to the v2 stuff please.

Documentation/admin-guide/cgroup-v2.rst
 
> > > That configurability is addressed by adding priority for soft limit
> > > reclaiming to make sure that no pages will be reclaimed from memcg of
> > > higer priortiy in favor of memcg of lower priority.
> > 
> > cgroup v1 interfaces are generally frozen and mostly aimed at backward
> > compatibility. I am especially concerned about adding a new way to
> > control soft limit which is known to be misdesigned and unfixable to
> > behave reasonably.
> >
> An URL to the drafts/works about the new way in your git tree.

Whut?
-- 
Michal Hocko
SUSE Labs