linux-kernel - Re: [PATCH] mm, slab: Extend slab/shrink to shrink all the memcg caches

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Date:   Tue, 2 Jul 2019 14:33:40 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>, linux-mm@...ck.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] mm, slab: Extend slab/shrink to shrink all the memcg
 caches

On Tue, 2 Jul 2019 16:44:24 -0400 Waiman Long <longman@...hat.com> wrote:

> On 7/2/19 4:03 PM, Andrew Morton wrote:
> > On Tue,  2 Jul 2019 14:37:30 -0400 Waiman Long <longman@...hat.com> wrote:
> >
> >> Currently, a value of '1" is written to /sys/kernel/slab/<slab>/shrink
> >> file to shrink the slab by flushing all the per-cpu slabs and free
> >> slabs in partial lists. This applies only to the root caches, though.
> >>
> >> Extends this capability by shrinking all the child memcg caches and
> >> the root cache when a value of '2' is written to the shrink sysfs file.
> > Why?
> >
> > Please fully describe the value of the proposed feature to or users. 
> > Always.
> 
> Sure. Essentially, the sysfs shrink interface is not complete. It allows
> the root cache to be shrunk, but not any of the memcg caches. 

But that doesn't describe anything of value.  Who wants to use this,
and why?  How will it be used?  What are the use-cases?