linux-ext4 - question about file space preallocation with fallocate

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Date:	Mon, 27 Dec 2010 14:47:50 +0000
From:	Filipe David Manana <fdmanana@...che.org>
To:	linux-ext4@...r.kernel.org
Subject: question about file space preallocation with fallocate

Hi,

I have been playing around with fallocate to preallocate space for a
file with the mode FALLOC_FL_KEEP_SIZE.
I'm running with Linux kernel 2.6.35-24 and ext4 as the fs.

I'm allocating 1Gb for a newly created file and then in a loop I write
1Gb of data into that file in chunks of 1Kb.
fallocate is returning me 0, therefore it was successful.
However I don't see any performance gains compared to a version of
that same code that doesn't call fallocate.

The test code which does this is:  http://friendpaste.com/2UR0n2U851u4IXmubeLZh0

Am I doing something wrong?

best regards,

-- 
Filipe David Manana,
fdmanana@...il.com, fdmanana@...che.org

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."
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