Red Hat Bugzilla – Bug 588930
umount performance on ext4 has regressed
Last modified: 2010-05-19 15:17:52 EDT
Description of problem: umount on ext4 has seriously regressed, stalling for over a minute (or more):
Version-Release number of selected component (if applicable): 2.6.33
How reproducible: always
Steps to Reproduce:
1. install a Fedora 13, accepted defaults.
2. Run the following as root:
dd if=/dev/zero of=test.ext4 bs=1 count=1 seek=1G
mkfs.ext4 -F test.ext4
mkdir -p /mnt/test
mount -o loop test.ext4 /mnt/test
echo $(seq 65536) | (cd /mnt/test; xargs touch)
time umount /mnt/test
Actual results: over a minute to perform umount.
Expected results: a few seconds.
Looks barrier related, if you change the mount -o loop to mount -o loop,nobarrier, it's speedy.
Author: Nikanth Karthikesan <firstname.lastname@example.org>
Date: Tue Mar 24 12:29:54 2009 +0100
loop: support barrier writes
Honour barrier requests in the loop back block device driver.
In case of barrier bios, flush the backing file once before processing the
barrier and once after to guarantee ordering. In case of filesystems that
does not support fsync, barrier bios would be failed with -EOPNOTSUPP.
Signed-off-by: Nikanth Karthikesan <email@example.com>
Signed-off-by: Jens Axboe <firstname.lastname@example.org>
So you're fsyncing the loop file 2x for each barrier, and those fsyncs in turn cause cache flushes on your underlying device; once upon a time lvm didn't do anything there, but now it does ... I think you're just getting bitten by the new and improved barrier support at every level.
Since this really seems to be an upstream-relevant bug motivated by an ubuntu bug that ubuntu seemed unable to solve, I'm going to close this as UPSTREAM and worry about it there, rather than working the ubuntu bug through the fedora bugzilla.
The mad skillz that did the new colour schemes for a new release of an os (Ubuntu 10.04) should be just as capable at being able to overcome the limitation of journal transaction and barrier blocks between every single inode update by breakfast.
kernel-188.8.131.52-95.fc13 has been submitted as an update for Fedora 13.
kernel-184.108.40.206-95.fc13 has been pushed to the Fedora 13 stable repository. If problems still persist, please make note of it in this bug report.