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    SubjectRe: ext3 IO latency measurements (was: Linux 2.6.29)
    On Fri, 27 Mar 2009 15:10:56 -0700 (PDT) Linus Torvalds <> wrote:

    > On Fri, 27 Mar 2009, Jan Kara wrote:
    > >
    > > Doable but not fairly simple ;) Firstly you have to restart a transaction
    > > when you've used up all the credits you originally started with (easy),
    > > secondly ext3 uses lock order PageLock -> "transaction start" which is
    > > unusable for the scheme you suggest. So we'd have to revert that - which
    > > needs larger audit of our locking scheme and that's probably the reason
    > > why noone has done it yet.
    > It's also not clear that ext3 can really do much better than the regular
    > generic_writepages() logic. I mean, seriously, what's there to improve on?

    - opening a single transaction for many pages in the cases when a
    transaction _is_ needed.

    - single large BIO versus zillions of single-page BIOs.

    Relatively minor benefits, but it's a bit odd that we never got around
    to doing it.

    It just got quite a bit harder to do, so I expect we won't be doing it.

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