linux-kernel - Re: [PATCH] Revert "mm/vmscan: never demote for memcg reclaim"

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Date:   Wed, 18 May 2022 12:51:10 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Johannes Weiner <hannes@...xchg.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        Zi Yan <ziy@...dia.com>, Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...com>
Subject: Re: [PATCH] Revert "mm/vmscan: never demote for memcg reclaim"

On 5/18/22 12:09, Johannes Weiner wrote:
> However, with NUMA balancing now doing tier promotions, demotion is
> part of the page aging process. Global reclaim demotes the coldest
> toptier pages to secondary memory, where their life continues and from
> which they have a chance to get promoted back. Essentially, tiered
> memory systems have an LRU order that spans multiple nodes.

Thanks for the detailed explanation.  Ultimately, this was just intended
as an optimization to make cgroup reclaim more efficient.  But, I agree
that ordering correctness should trump efficiency.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>