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Date:   Fri, 28 Jun 2019 15:32:28 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Roman Gushchin <guro@fb.com>
cc:     Waiman Long <longman@redhat.com>,
        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>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
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        Shakeel Butt <shakeelb@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 2/2] mm, slab: Extend vm/drop_caches to shrink kmem
 slabs
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On Thu, 27 Jun 2019, Roman Gushchin wrote:

> so that objects belonging to different memory cgroups can share the same page
> and kmem_caches.
>
> It's a fairly big change though.

Could this be done at another level? Put a cgoup pointer into the
corresponding structures and then go back to just a single kmen_cache for
the system as a whole? You can still account them per cgroup and there
will be no cleanup problem anymore. You could scan through a slab cache
to remove the objects of a certain cgroup and then the fragmentation
problem that cgroups create here will be handled by the slab allocators in
the traditional way. The duplication of the kmem_cache was not designed
into the allocators but bolted on later.