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Re: Bug#605009: serious performance regression with ext4



Hi,

On Tue, 30 Nov 2010, Michael Biebl wrote:
> Something interesting I noticed:
> 
> I created the ext4 file system on a spare partition and installed a chroot.
> After running the test, I exited the chroot, immediately unmounted the partition
> and measured how long it took:
> 
> 1.15.8.5: 0.4s

Expected, this version calls sync() so there's nothing to write back when
you umount the filesystem.

> 1.15.8.6: 7.2s
> 1.15.8.6+patch: 18.4s

I can't explain the difference between both but it doesn't matter much IMO.

> If I wait a bit (+60s) after exiting the chroot and then do the unmount, it is
> almost instant (< 0.2s) in all three cases.

60s is more than the default writeback delay so again it's normal.

$ sudo cat /proc/sys/vm/dirty_writeback_centisecs
500

 -> writeback after 5 sec

Cheers,
-- 
Raphaël Hertzog ◈ Debian Developer

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                      ▶ http://RaphaelHertzog.fr (Français)


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