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Subject: Re: [PATCH -V11 8/9] mm/vmscan: never demote for memcg reclaim
To:     Zi Yan <ziy@nvidia.com>, Huang Ying <ying.huang@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Yang Shi <shy828301@gmail.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>
References: <20210721063926.3024591-1-ying.huang@intel.com>
 <20210721063926.3024591-8-ying.huang@intel.com>
 <43A1CB83-6127-427F-94AF-40CE1B283BE1@nvidia.com>
From:   Dave Hansen <dave.hansen@intel.com>
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Message-ID: <59a92898-4a8a-05d3-5f75-1f8defb6feda@intel.com>
Date:   Wed, 21 Jul 2021 14:58:05 -0700
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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.