Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210721063926.3024591-1-ying.huang@intel.com>
 <20210721063926.3024591-8-ying.huang@intel.com> <43A1CB83-6127-427F-94AF-40CE1B283BE1@nvidia.com>
 <59a92898-4a8a-05d3-5f75-1f8defb6feda@intel.com>
In-Reply-To: <59a92898-4a8a-05d3-5f75-1f8defb6feda@intel.com>
From:   Yang Shi <shy828301@gmail.com>
Date:   Wed, 21 Jul 2021 15:03:56 -0700
Message-ID: <CAHbLzkoBUCNqD1DVhsToCe457v=rBQCm2=4Ezyjb7-6wuNr+LQ@mail.gmail.com>
Subject: Re: [PATCH -V11 8/9] mm/vmscan: never demote for memcg reclaim
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Zi Yan <ziy@nvidia.com>, Huang Ying <ying.huang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Michal Hocko <mhocko@suse.com>, Wei Xu <weixugc@google.com>,
        Oscar Salvador <osalvador@suse.de>,
        David Rientjes <rientjes@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Greg Thelen <gthelen@google.com>,
        Keith Busch <kbusch@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Jul 21, 2021 at 2:58 PM Dave Hansen <dave.hansen@intel.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@linux.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.