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Date:   Wed, 3 Jul 2019 16:10:31 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Waiman Long <longman@redhat.com>
cc:     Michal Hocko <mhocko@kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        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>,
        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
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On Wed, 3 Jul 2019, Waiman Long wrote:

> On 7/3/19 2:56 AM, Michal Hocko wrote:
> > On Tue 02-07-19 14:37:30, Waiman Long 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 do we need a new value for this functionality? I would tend to think
> > that skipping memcg caches is a bug/incomplete implementation. Or is it
> > a deliberate decision to cover root caches only?
>
> It is just that I don't want to change the existing behavior of the
> current code. It will definitely take longer to shrink both the root
> cache and the memcg caches. If we all agree that the only sensible
> operation is to shrink root cache and the memcg caches together. I am
> fine just adding memcg shrink without changing the sysfs interface
> definition and be done with it.

I think its best and consistent behavior to shrink all memcg caches
with the root cache. This looks like an oversight and thus a bugfix.