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

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Message-ID: <0100016bb89a0a6e-99d54043-4934-420f-9de0-1f71a8f943a3-000000@email.amazonses.com>
Date:   Wed, 3 Jul 2019 16:10:31 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Waiman Long <longman@...hat.com>
cc:     Michal Hocko <mhocko@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        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 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.