linux-ext4 - Re: [PATCH] ext4: start seraching for the right extent from the goal group.

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Message-ID: <20080501153747.GA7005@skywalker>
Date:	Thu, 1 May 2008 21:07:47 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	adilger@....com, linux-ext4@...r.kernel.org, cmm@...ibm.com,
	tytso@....edu
Subject: Re: [PATCH] ext4: start seraching for the right extent from the
	goal group.

On Wed, Apr 30, 2008 at 07:58:35AM -0500, Eric Sandeen wrote:
> Aneesh Kumar K.V wrote:
> > With mballoc we search for the best extent using different
> > criteria. We should always use the goal group when we are
> > starting with a new criteria.
> 
> Aneesh, is there any testcase etc that will demonstrate the resulting
> difference in layout?
> 
> It's not clear to me from this changelog (without looking at a lot more
> context) exactly what you're changing and why...

I don't have any specific test case.  With mballoc depending on the
request size we follow different criteria to allocate blocks. For
example if the size is stripe size multiple we use criteria 1 and start
searching for the right blocks from block group starting with goal
group. If we don't find right count of blocks, we use criteria 2 and start
searching from the group block 0. I guess with criteria 2 also, we should start
searching from the goal group so that when we find the right count of
blocks we find them close to the goal group.

-aneesh
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