linux-ext4 - Re: [PATCH] ext4: zero out small extents when writing to prealloc area.

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Message-id: <20080305064517.GB3616@webber.adilger.int>
Date:	Tue, 04 Mar 2008 23:45:17 -0700
From:	Andreas Dilger <adilger@....com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: zero out small extents when writing to prealloc	area.

On Mar 04, 2008  16:51 -0800, Mingming Cao wrote:
> On Tue, 2008-03-04 at 18:16 +0530, Aneesh Kumar K.V wrote:
> > +	/* If extent has less than 2*EXT4_EXT_ZERO_LEN zerout directly */
> > +	if (ee_len <= 2*EXT4_EXT_ZERO_LEN) {
> 
> Hmm, here this is range is extended to 2*EXT4_EXT_ZERO_LEN? I am a
> little more biased to keep the threshold constant as EXT4_EXT_ZERO_LEN
> around all places...

I initially thoguht this also, but it makes sense.  If the extent is
<= 2x EXT4_EXT_ZERO_LEN and it is split anywhere then the resulting
parts will be < EXT4_EXT_ZERO_LEN themselves, unless split is very
close to one edge.  Even then it is better to keep a single initialized
extent instead of 3 different ones.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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