linux-ext4 - Re: ext4

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Message-ID: <20120626185949.GB26669@thunk.org>
Date:	Tue, 26 Jun 2012 14:59:49 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Fredrick <fjohnber@...o.com>
Cc:	Ric Wheeler <rwheeler@...hat.com>, linux-ext4@...r.kernel.org,
	Andreas Dilger <adilger@...ger.ca>, wenqing.lz@...bao.com
Subject: Re: ext4_fallocate

On Tue, Jun 26, 2012 at 11:05:40AM -0700, Fredrick wrote:
> 
> I had run perf stat on ext4 functions between two runs of our program
> writing data to a file for the first time and writing data to the file
> for the second time(where the extents are initialized).

>From your mballoc differences, it sounds like you were comparing
fallocate with not using fallocate at all; is that right?

The comparison you need to do is using normal fallocate versus
fallocate with the no-hide-stale feature enabled.  It's obvious that
allocating blocks as you need will always be more expensive than using
fallocate.

						- Ted
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