linux-kernel - Re: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node

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Date:   Wed, 27 Mar 2019 10:05:48 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Zi Yan <ziy@...dia.com>, Keith Busch <kbusch@...nel.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, mhocko@...e.com,
        mgorman@...hsingularity.net, riel@...riel.com, hannes@...xchg.org,
        akpm@...ux-foundation.org, "Busch, Keith" <keith.busch@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Wu, Fengguang" <fengguang.wu@...el.com>,
        "Du, Fan" <fan.du@...el.com>, "Huang, Ying" <ying.huang@...el.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node

On 3/27/19 10:00 AM, Zi Yan wrote:
> I ask this because I observe that migrating a list of pages can
> achieve higher throughput compared to migrating individual page.
> For example, migrating 512 4KB pages can achieve ~750MB/s
> throughput, whereas migrating one 4KB page might only achieve
> ~40MB/s throughput. The experiments were done on a two-socket
> machine with two Xeon E5-2650 v3 @ 2.30GHz across the QPI link.

What kind of migration?

If you're talking about doing sys_migrate_pages() one page at a time,
that's a world away from doing something inside of the kernel one page
at a time.