linux-kernel - Re: [RFC PATCH] mm: migrate: Add new node demotion strategy

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Message-ID: <87fss7w3b7.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Mon, 08 Nov 2021 14:48:28 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc:     Dave Hansen <dave.hansen@...el.com>, <akpm@...ux-foundation.org>,
        <dave.hansen@...ux.intel.com>, <ziy@...dia.com>,
        <osalvador@...e.de>, <shy828301@...il.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm: migrate: Add new node demotion strategy

Baolin Wang <baolin.wang@...ux.alibaba.com> writes:

> On 2021/11/7 23:20, Dave Hansen wrote:
>> On 11/7/21 1:33 AM, Baolin Wang wrote:
>>> Thanks for your suggestion. After some thinking, can we change the
>>> node_demotion[] structure like below? Which means one source node can be
>>> demoted to mutiple target node, and we can set up the target node mask
>>> according to the node distance. How do you think? Thanks.
>>>
>>> static nodemask_t node_demotion[MAX_NUMNODES] __read_mostly =
>>>          {[0 ...  MAX_NUMNODES - 1] = NODE_MASK_NONE};
>> How large is that in the worst case?
>
> For the worst case (MAX_NUMNODES=1024), the size of the node_demotion
> is 131072 bytes, while the size of original data structure is 4096
> bytes. Maybe we can allocate the node_demotion dynamically?

Per my understanding, in most cases, the number of demotion target nodes
should be quite small.  So why not restrict the number of demotion
target nodes to make it some kind of simple array?

Best Regards,
Huang, Ying