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    SubjectRe: ext3 IO latency measurements (was: Linux 2.6.29)
    On Thu 26-03-09 15:57:25, Andrew Morton wrote:
    > On Thu, 26 Mar 2009 15:39:53 -0700 (PDT) Linus Torvalds <> wrote:
    > > On Thu, 26 Mar 2009, Jan Kara wrote:
    > > >
    > > > Reads are measurably better with the patch - the test with cat you
    > > > describe below took ~0.5s per file without the patch and always less than
    > > > 0.02s with the patch. So it seems to help something.
    > >
    > > That would seem to be a _huge_ improvement.
    > It's strange that we still don't have an ext3_writepages(). Open a
    > transaction, do a large pile of writes, close the transaction again.
    > We don't even have a data=writeback writepages() implementation, which
    > should be fairly simple.
    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.

    > Bizarre.
    > Mingming had a shot at it a few years ago and I think Badari did as
    > well, but I guess it didn't work out.
    > Falling back to generic_writepages() on our main local fs is a bit lame.

    Jan Kara <>
    SUSE Labs, CR

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