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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 25 Jun 2019 17:15:48 -0700
Message-ID: <CALvZod4YoO0eoQmocHEFP7zrYpf3SzvaBEDpfDHS=_fiCyYcAA@mail.gmail.com>
Subject: Re: [PATCH v7 09/10] mm: stop setting page->mem_cgroup pointer for
 slab pages
To:     Roman Gushchin <guro@fb.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kernel Team <kernel-team@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Waiman Long <longman@redhat.com>
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On Tue, Jun 11, 2019 at 4:18 PM Roman Gushchin <guro@fb.com> wrote:
>
> Every slab page charged to a non-root memory cgroup has a pointer
> to the memory cgroup and holds a reference to it, which protects
> a non-empty memory cgroup from being released. At the same time
> the page has a pointer to the corresponding kmem_cache, and also
> hold a reference to the kmem_cache. And kmem_cache by itself
> holds a reference to the cgroup.
>
> So there is clearly some redundancy, which allows to stop setting
> the page->mem_cgroup pointer and rely on getting memcg pointer
> indirectly via kmem_cache. Further it will allow to change this
> pointer easier, without a need to go over all charged pages.
>
> So let's stop setting page->mem_cgroup pointer for slab pages,
> and stop using the css refcounter directly for protecting
> the memory cgroup from going away. Instead rely on kmem_cache
> as an intermediate object.
>
> Make sure that vmstats and shrinker lists are working as previously,
> as well as /proc/kpagecgroup interface.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>