linux-kernel - Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node

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Date:   Tue, 16 Apr 2019 16:17:44 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     mgorman@...hsingularity.net, riel@...riel.com, hannes@...xchg.org,
        akpm@...ux-foundation.org, keith.busch@...el.com,
        dan.j.williams@...el.com, fengguang.wu@...el.com, fan.du@...el.com,
        ying.huang@...el.com, ziy@...dia.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v2 RFC PATCH 0/9] Another Approach to Use PMEM as NUMA Node



On 4/16/19 4:04 PM, Dave Hansen wrote:
> On 4/16/19 2:59 PM, Yang Shi wrote:
>> On 4/16/19 2:22 PM, Dave Hansen wrote:
>>> Keith Busch had a set of patches to let you specify the demotion order
>>> via sysfs for fun.  The rules we came up with were:
>>> 1. Pages keep no history of where they have been
>>> 2. Each node can only demote to one other node
>> Does this mean any remote node? Or just DRAM to PMEM, but remote PMEM
>> might be ok?
> In Keith's code, I don't think we differentiated.  We let any node
> demote to any other node you want, as long as it follows the cycle rule.

I recall Keith's code let the userspace define the target node. Anyway, 
we may need add one rule: not migrate-on-reclaim from PMEM node. 
Demoting from PMEM to DRAM sounds pointless.