linux-kernel - Re: [PATCH -V11 8/9] mm/vmscan: never demote for memcg reclaim

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Date:   Wed, 21 Jul 2021 14:58:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Zi Yan <ziy@...dia.com>, Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Yang Shi <shy828301@...il.com>, Michal Hocko <mhocko@...e.com>,
        Wei Xu <weixugc@...gle.com>,
        Oscar Salvador <osalvador@...e.de>,
        David Rientjes <rientjes@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Greg Thelen <gthelen@...gle.com>,
        Keith Busch <kbusch@...nel.org>
Subject: Re: [PATCH -V11 8/9] mm/vmscan: never demote for memcg reclaim

On 7/21/21 2:38 PM, Zi Yan wrote:
> On 21 Jul 2021, at 2:39, Huang Ying wrote:
>> From: Dave Hansen <dave.hansen@...ux.intel.com>
>>
>> Global reclaim aims to reduce the amount of memory used on a
>> given node or set of nodes.  Migrating pages to another node
>> serves this purpose.
>>
>> memcg reclaim is different.  Its goal is to reduce the total
>> memory consumption of the entire memcg, across all nodes.
>> Migration does not assist memcg reclaim because it just moves
>> page contents between nodes rather than actually reducing memory
>> consumption.
...
> Should this be folded into Patch 4 when can_demote() is
> introduced?

I guess it could be.  But, it's logically separate since it has its
own justification which is rather discrete.

I think it's best to keep it separate.