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    SubjectRe: Extending page pinning into fs/direct-io.c
    On Thu, May 25, 2023 at 10:01 AM David Howells <dhowells@redhat.com> wrote:
    >
    > What do we gain from it? Presumably since nothing is supposed to write to
    > that page, it can be shared in all the caches.

    I don't remember the details, but they went something like "broken
    purely virtually indexed cache avoids physical aliases by cacheline
    exclusion at fill time".

    Which then meant that if you walk a zero mapping, you'll invalidate
    the caches of the previous page when you walk the next one. Causing
    horrendously bad performance.

    Unless it's colored.

    Something like that. I probably got all the details wrong.

    Linus

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