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    SubjectRe: [RFC patch 0/5] futex: Allow lockless empty check of hashbucket plist in futex_wake()

    * Linus Torvalds <torvalds@linux-foundation.org> wrote:

    > On Sun, Dec 1, 2013 at 8:55 AM, Ingo Molnar <mingo@kernel.org> wrote:
    > >
    > > Keeping the page invariant would bring significant performance
    > > advantages to hashing.
    >
    > Or not. Rather, it would make things much worse. The virtual address
    > is much simpler and better to avoid needing any page table lookup
    > etc crap. The key is just the mm and the virtual address, and no
    > silly page table walks etc necessary.

    In theory the CPU could give us the phyisical page address, as the TLB
    is already there: for most futex ops when the kernel runs we just
    attempted access of the virtual address on the user-space side, so the
    hardware already did the hard work of looking up everything in the
    page tables and has it cached most likely.

    But yeah, you are right :-/

    Thanks,

    ngo


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