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    SubjectRe: [patch 1/2] fs: mnt_want_write speedup
    On Thu, Apr 02, 2009 at 08:22:10PM +0200, Nick Piggin wrote:
    > On Wed, Mar 18, 2009 at 12:13:43PM -0700, Dave Hansen wrote:
    > > On Thu, 2009-03-12 at 05:13 +0100, Nick Piggin wrote:
    > > > On Wed, Mar 11, 2009 at 03:11:17PM -0700, Dave Hansen wrote:
    > > > > I'm feeling a bit better about these, although I am still honestly quite
    > > > > afraid of the barriers. I also didn't like all the #ifdefs much, but
    > > > > here's some help on that.
    > > >
    > > > FWIW, we have this in suse kernels because page fault performance was
    > > > so bad compared with SLES10. mnt_want_write & co was I think the 2nd
    > > > biggest offender for file backed mappings (after pvops). I think we're
    > > > around parity again even with pvops.
    > >
    > > Page faults themselves? Which path was that from?
    >
    > Yes. file_update_time.

    FWIW, I'm not sure that this optimization is valid. We might eventually
    want to go for "don't allow any new writers, remount r/o when existing
    ones expire" functionality, so nested mnt_want_write() might eventually
    be allowed to fail.


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