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

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Message-ID: <CAHbLzkoBUCNqD1DVhsToCe457v=rBQCm2=4Ezyjb7-6wuNr+LQ@mail.gmail.com>
Date:   Wed, 21 Jul 2021 15:03:56 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Zi Yan <ziy@...dia.com>, Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Yang Shi <yang.shi@...ux.alibaba.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 Wed, Jul 21, 2021 at 2:58 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> 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.

Yes, I agree.