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

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Message-ID: <7cb4e229-a1a9-e236-f806-926351a917cc@intel.com>
Date:   Wed, 27 Mar 2019 13:40:07 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 1:35 PM, Matthew Wilcox wrote:
> 
> pmem1 --- node1 --- node2 --- pmem2
>             |   \ /   |
>             |    X    |
>             |   / \   |
> pmem3 --- node3 --- node4 --- pmem4
> 
> which I could actually see someone building with normal DRAM, and we
> should probably handle the same way as pmem; for a process running on
> node3, allocate preferentially from node3, then pmem3, then other nodes,
> then other pmems.

That makes sense.  But, it might _also_ make sense to fill up all DRAM
first before using any pmem.  That could happen if the NUMA interconnect
is really fast and pmem is really slow.

Basically, with the current patches we are depending on the firmware to
"nicely" enumerate the topology and we're keeping the behavior that we
end up with, for now, whatever it might be.

Now, let's sit back and see how nice the firmware is. :)