linux-kernel - Re: [PATCH v4 01/17] mm: list_lru: optimize memory consumption of arrays of per cgroup lists

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Date:   Wed, 15 Dec 2021 20:09:10 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...com>, Yang Shi <shy828301@...il.com>,
        Alex Shi <alexs@...nel.org>,
        Wei Yang <richard.weiyang@...il.com>,
        Dave Chinner <david@...morbit.com>,
        trond.myklebust@...merspace.com, anna.schumaker@...app.com,
        jaegeuk@...nel.org, chao@...nel.org,
        Kari Argillander <kari.argillander@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-nfs@...r.kernel.org, Qi Zheng <zhengqi.arch@...edance.com>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        fam.zheng@...edance.com, Muchun Song <smuchun@...il.com>
Subject: Re: [PATCH v4 01/17] mm: list_lru: optimize memory consumption of
 arrays of per cgroup lists

On Tue, Dec 14, 2021 at 9:38 PM Johannes Weiner <hannes@...xchg.org> wrote:
>
> On Tue, Dec 14, 2021 at 12:53:26AM +0800, Muchun Song wrote:
> > The list_lru uses an array (list_lru_memcg->lru) to store pointers
> > which point to the list_lru_one. And the array is per memcg per node.
> > Therefore, the size of the arrays will be 10K * number_of_node * 8 (
> > a pointer size on 64 bits system) when we run 10k containers in the
> > system. The memory consumption of the arrays becomes significant. The
> > more numa node, the more memory it consumes.
>
> The complexity for the lists themselves is still nrmemcgs * nrnodes
> right? But the rcu_head goes from that to nrmemcgs.

Right.

>
> > I have done a simple test, which creates 10K memcg and mount point
> > each in a two-node system. The memory consumption of the list_lru
> > will be 24464MB. After converting the array from per memcg per node
> > to per memcg, the memory consumption is going to be 21957MB. It is
> > reduces by 2.5GB. In our AMD servers, there are 8 numa nodes in
> > those system, the memory consumption could be more significant.
>
> The code looks good to me, but it would be useful to include a
> high-level overview of the new scheme, explain that the savings come
> from the rcu heads, that it simplifies the alloc/dealloc path etc.

Will do in the next version.

>
> With that,
>
> > Signed-off-by: Muchun Song <songmuchun@...edance.com>

Thanks.

>
> Acked-by: Johannes Weiner <hannes@...xchg.org>