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    SubjectRe: [PATCH RFC] x86: avoid atomic operation in test_and_set_bit_lock if possible
    On Fri, Mar 25, 2011 at 3:06 AM, Jan Beulich <JBeulich@novell.com> wrote:
    >
    > The problem was observed with __lock_page() (in a variant not
    > upstream for reasons not known to me), and prefixing e.g.
    > trylock_page() with an extra PageLocked() check yielded the
    > below quoted improvements.

    Ok. __lock_page() _definitely_ should do the test_bit() thing first,
    because it's normally called from lock_page() that has already tested
    the bit.

    But it already seems to do that, so I'm wondering what your variant is.

    I'm also a bit surprised that lock_page() is that hot (unless your
    _lock_page() variant is simply too broken and ends up spinning?).
    Maybe we have some path that takes the page lock unnecessarily? What's
    the load?

    Linus


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