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Date:   Tue, 2 Jul 2019 14:33:40 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Jonathan Corbet <corbet@lwn.net>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>, linux-mm@kvack.org,
        linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        Roman Gushchin <guro@fb.com>,
        Shakeel Butt <shakeelb@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH] mm, slab: Extend slab/shrink to shrink all the memcg
 caches
Message-Id: <20190702143340.715f771192721f60de1699d7@linux-foundation.org>
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        <20190702130318.39d187dc27dbdd9267788165@linux-foundation.org>
        <78879b79-1b8f-cdfd-d4fa-610afe5e5d48@redhat.com>
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On Tue, 2 Jul 2019 16:44:24 -0400 Waiman Long <longman@redhat.com> wrote:

> On 7/2/19 4:03 PM, Andrew Morton wrote:
> > On Tue,  2 Jul 2019 14:37:30 -0400 Waiman Long <longman@redhat.com> wro=
te:
> >
> >> 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.=20
> > Always.
>=20
> Sure. Essentially, the sysfs shrink interface is not complete. It allows
> the root cache to be shrunk, but not any of the memcg caches.=A0

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?