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    SubjectRe: [rfc] lru_add_drain_all() vs isolation
    > The usefulness of a scheme like this requires:
    > 1. There are cpus that continually execute user space code
    > without system interaction.
    > 2. There are repeated VM activities that require page isolation /
    > migration.
    > The first page isolation activity will then clear the lru caches of the
    > processes doing number crunching in user space (and therefore the first
    > isolation will still interrupt). The second and following isolation will
    > then no longer interrupt the processes.
    > 2. is rare. So the question is if the additional code in the LRU handling
    > can be justified. If lru handling is not time sensitive then yes.

    Christoph, I'd like to discuss a bit related (and almost unrelated) thing.
    I think page migration don't need lru_add_drain_all() as synchronous, because
    page migration have 10 times retry.

    Then asynchronous lru_add_drain_all() cause

    - if system isn't under heavy pressure, retry succussfull.
    - if system is under heavy pressure or RT-thread work busy busy loop, retry failure.

    I don't think this is problematic bahavior. Also, mlock can use asynchrounous lru drain.

    What do you think?

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