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    SubjectRe: [PATCH 06/10] mm: vmscan: demote anon DRAM pages to PMEM node
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    On 27 Mar 2019, at 6:08, Keith Busch wrote:

    > On Tue, Mar 26, 2019 at 08:41:15PM -0700, Yang Shi wrote:
    >> On 3/26/19 5:35 PM, Keith Busch wrote:
    >>> migration nodes have higher free capacity than source nodes. And since
    >>> your attempting THP's without ever splitting them, that also requires
    >>> lower fragmentation for a successful migration.
    >>
    >> Yes, it is possible. However, migrate_pages() already has logic to
    >> handle such case. If the target node has not enough space for migrating
    >> THP in a whole, it would split THP then retry with base pages.
    >
    > Oh, you're right, my mistake on splitting. So you have a good best effort
    > migrate, but I still think it can fail for legitimate reasons that should
    > have a swap fallback.

    Does this mean we might want to factor out the page reclaim code in shrink_page_list()
    and call it for each page, which fails to migrate to PMEM. Or do you still prefer
    to migrate one page at a time, like what you did in your patch?

    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.


    --
    Best Regards,
    Yan Zi
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