linux-kernel - Re: [PATCH 2/2] mm, slab: Extend vm/drop

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Message-ID: <0100016b9eb7685e-0a5ab625-abb4-4e79-ab86-07744b1e4c3a-000000@email.amazonses.com>
Date:   Fri, 28 Jun 2019 15:32:28 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Roman Gushchin <guro@...com>
cc:     Waiman Long <longman@...hat.com>,
        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>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 2/2] mm, slab: Extend vm/drop_caches to shrink kmem
 slabs

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.