linux-ext4 - [PATCH 0/2] ext3 data=guarded

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Date:	Tue, 14 Apr 2009 16:57:13 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: [PATCH 0/2] ext3 data=guarded

Hello everyone,

Here is the ext3 data=guarded code again, this time it has passed some
basic tests.  It should safely leave non data=guarded mounts alone and
only be dangerous when the new code is turned on (I hope).

On the performance side, it runs the same as data=writeback, except when
you're making files with holes where it runs the same as data=ordered.

There's definitely more CPU time involved with tracking the data=guarded
buffer heads and updating i_size when the IO is over, but at least on my
5 drive array that doesn't show up.

For the fsync + background streaming write workload, data=guarded does
fsync's in 0.8s, just like data=writeback.  data=ordered on the same
test was doing between 5 and 30s per fsync, so it seems I've fixed that
part at least.

The next step is much more testing (blocksize != pagesize among others)
and much more review.  But, I'm hoping for some feedback first on if
this is a direction we want to take the ext3 code.

The diffstat looks scary, but lots of the changes are comments...

-chris

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