linux-ext4 - Re: [PATCH v2] ext4: Transfer initialized block to right neighbor if possible

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Message-ID: <20130401151216.GC4731@thunk.org>
Date:	Mon, 1 Apr 2013 11:12:16 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, darrick.wong@...cle.com
Subject: Re: [PATCH v2] ext4: Transfer initialized block to right neighbor if
 possible

On Wed, Mar 20, 2013 at 03:53:55PM +0100, Lukas Czerner wrote:
> Currently when converting extent to initialized we attempt to transfer
> initialized block to the left neighbour if possible when certain criteria
> are met. However we do not attempt to do the same for the right
> neighbor.
> 
> This commit adds the possibility to transfer initialized block to the
> right neighbour if:
> 
> 1. We're not converting the whole extent
> 2. Both extents are stored in the same extent tree node
> 3. Right neighbor is initialized
> 4. Right neighbor is logically abutting the current one
> 5. Right neighbor is physically abutting the current one
> 6. Right neighbor would not overflow the length limit
> 
> This is basically the same logic as with transferring to the left. This
> will gain us some performance benefits since it is faster than inserting
> extent and then merging it.
> 
> It would also prevent some situation in delalloc patch when we might run
> out of metadata reservation. This is due to the fact that we would
> attempt to split the extent first (possibly allocating new metadata
> block) even though we did not counted for that because it can (and will)
> be merged again. This commit fix that scenario, because we no longer
> need to split the extent in such case.
> 
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>

Thanks, applied to the dev branch for testing

					- Ted
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