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

From: Waiman Long <longman@redhat.com>
To: Christopher Lameter <cl@linux.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
Date: Wed, 3 Jul 2019 12:13:15 -0400	[thread overview]
Message-ID: <1afc4772-27e5-b7f1-a15e-e912e15737e6@redhat.com> (raw)
In-Reply-To: <0100016bb89a0a6e-99d54043-4934-420f-9de0-1f71a8f943a3-000000@email.amazonses.com>

On 7/3/19 12:10 PM, Christopher Lameter wrote:
> 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.
>
Yes, that is what I am now planning to do for the next version of the patch.

Cheers,
Longman