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    SubjectRe: ext4 performance regression 2.6.27-stable versus 2.6.32 and later
    On Fri, Jul 30, 2010 at 11:01:36PM +0200, Kay Diederichs wrote:
    > whereas for the result is typically
    > Filesystem type is: ef53
    > File size of
    > /mnt/md5/scratch/nfs-test/tmp/xds/frames/h2g28_1_00000.cbf is
    > 6229688 (1521 blocks, blocksize 4096)
    > ext logical physical expected length flags
    > 0 0 826376200 1521 eof
    > /mnt/md5/scratch/nfs-test/tmp/xds/frames/h2g28_1_00000.cbf: 1 extent found

    OK, so 2.6.32 is actually doing a better job laying out the files....

    The blktrace will be interesting, but at this point I'm wondering if
    this is a generic kernel-wide writeback regression. At $WORK we've
    noticed some performance regressions between 2.6.26-based kernels and
    2.6.33- and 2.6.34-based kernels with both ext2 and ext4 (in no
    journal mode) that we've been trying to track down. We have a pretty
    large number of patches applied to both 2.6.26 and 2.6.33/34 which is
    why I haven't mentioned it up until now, but at this point it seems
    pretty clear there are some writeback issues in the mainline kernel.

    There are half a dozen or so patch series on LKML that are addressing
    writeback in one way or another, and writeback is a major topic at the
    upcoming Linux Storage and Filesystem workshop. So if this is the
    cause, hopefully there will be some improvements in this area in the
    near future.

    - Ted

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