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    SubjectRe: Unexpected splice "always copy" behavior observed


    On Thu, 20 May 2010, Nick Piggin wrote:
    >
    > Well I mean a full invalidate -- invalidate_mapping_pages -- so there is
    > literally no pagecache there at all.

    Umm. That won't work. Think mapped pages. You can't handle them
    atomically, so somebody will page-fault them in.

    So you'd have to have a "invalidate_and_replace()" to do it atomically
    while holding the mapping spinlock or something.

    And WHAT IS THE POINT? That will be about a million times slower than
    just doing the effing copy in the first place!

    Memory copies are _not_ slow. Not compared to taking locks and doing TLB
    invalidates.

    Linus


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