linux-ext4 - ext4 and dir_index optimization

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Date:	Sun, 22 May 2011 14:52:37 +0200
From:	Nikola Ciprich <nikola.ciprich@...uxbox.cz>
To:	linux ext4 list <linux-ext4@...r.kernel.org>
Cc:	nikola.ciprich@...uxbox.cz,
	Petr Kopecký <petr.kopecky@...uxbox.cz>
Subject: ext4 and dir_index optimization

Hello everybody,

I'd like to ask few questions about dir_index on ext4. On one of my servers
running 2.6.32.14, we were experiencing performance problems, especially
accessing directory with huge (hundreds of thousands) amount of files
was pain. The filesystem had dir_index enabled, so I tried running fsck
-D on it in order to force reindexation. It helped A LOT - ls -1 on this
directory took about 5 minutes, after reindexation, it took about 10
seconds!
So my question is - is it really needed to force reindexation from time
to time? I'm pretty sure dir_index has been enabled since the creation of
filesystem, so shouldn't index be maintained automatically?
Is it possible to check somehow whether optimization is needed, without
umounting fs and running fsck? And possibly also do this optimization?

Thanks a lot in advance!

Cheers!

nik



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