linux-kernel - Re: [RFC PATCH 0/10] Another Approach to Use PMEM as NUMA Node

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Date:   Thu, 28 Mar 2019 11:58:57 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Keith Busch <keith.busch@...el.com>,
        Fengguang Wu <fengguang.wu@...el.com>,
        "Du, Fan" <fan.du@...el.com>, "Huang, Ying" <ying.huang@...el.com>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/10] Another Approach to Use PMEM as NUMA Node



On 3/27/19 11:58 PM, Michal Hocko wrote:
> On Wed 27-03-19 19:09:10, Yang Shi wrote:
>> One question, when doing demote and promote we need define a path, for
>> example, DRAM <-> PMEM (assume two tier memory). When determining what nodes
>> are "DRAM" nodes, does it make sense to assume the nodes with both cpu and
>> memory are DRAM nodes since PMEM nodes are typically cpuless nodes?
> Do we really have to special case this for PMEM? Why cannot we simply go
> in the zonelist order? In other words why cannot we use the same logic
> for a larger NUMA machine and instead of swapping simply fallback to a
> less contended NUMA node? It can be a regular DRAM, PMEM or whatever
> other type of memory node.

Thanks for the suggestion. It makes sense. However, if we don't 
specialize a pmem node, its fallback node may be a DRAM node, then the 
memory reclaim may move the inactive page to the DRAM node, it sounds 
not make too much sense since memory reclaim would prefer to move 
downwards (DRAM -> PMEM -> Disk).

Yang