linux-kernel - Re: [PATCH v3] mm: Add nodes= arg to memory.reclaim

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Date:   Fri, 2 Dec 2022 15:51:05 -0800
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Mina Almasry <almasrymina@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Huang Ying <ying.huang@...el.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Yosry Ahmed <yosryahmed@...gle.com>, weixugc@...gle.com,
        fvdl@...gle.com, Michal Hocko <mhocko@...e.com>,
        bagasdotme@...il.com, cgroups@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3] mm: Add nodes= arg to memory.reclaim

On Fri, Dec 2, 2022 at 2:37 PM Mina Almasry <almasrymina@...gle.com> wrote:
>
> The nodes= arg instructs the kernel to only scan the given nodes for
> proactive reclaim. For example use cases, consider a 2 tier memory system:
>
> nodes 0,1 -> top tier
> nodes 2,3 -> second tier
>
> $ echo "1m nodes=0" > memory.reclaim
>
> This instructs the kernel to attempt to reclaim 1m memory from node 0.
> Since node 0 is a top tier node, demotion will be attempted first. This
> is useful to direct proactive reclaim to specific nodes that are under
> pressure.
>
> $ echo "1m nodes=2,3" > memory.reclaim
>
> This instructs the kernel to attempt to reclaim 1m memory in the second tier,
> since this tier of memory has no demotion targets the memory will be
> reclaimed.
>
> $ echo "1m nodes=0,1" > memory.reclaim
>
> Instructs the kernel to reclaim memory from the top tier nodes, which can
> be desirable according to the userspace policy if there is pressure on
> the top tiers. Since these nodes have demotion targets, the kernel will
> attempt demotion first.
>
> Since commit 3f1509c57b1b ("Revert "mm/vmscan: never demote for memcg
> reclaim""), the proactive reclaim interface memory.reclaim does both
> reclaim and demotion. Reclaim and demotion incur different latency costs
> to the jobs in the cgroup. Demoted memory would still be addressable
> by the userspace at a higher latency, but reclaimed memory would need to
> incur a pagefault.
>
> The 'nodes' arg is useful to allow the userspace to control demotion
> and reclaim independently according to its policy: if the memory.reclaim
> is called on a node with demotion targets, it will attempt demotion first;
> if it is called on a node without demotion targets, it will only attempt
> reclaim.
>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>
>

Acked-by: Shakeel Butt <shakeelb@...gle.com>