linux-ext4 - Re: [RFC][PATCH] Set JBD2_FEATURE_INCOMPAT_64BIT on filesystems larger than 32-bit blocks (take 2).

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Date:	Tue, 5 Jun 2007 14:58:14 -0500
From:	"Jose R. Santos" <jrs@...ibm.com>
To:	cmm@...ibm.com
Cc:	Laurent Vivier <Laurent.Vivier@...l.net>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Andreas Dilger <adilger@...sterfs.com>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [RFC][PATCH] Set JBD2_FEATURE_INCOMPAT_64BIT on filesystems
 larger than 32-bit blocks (take 2).

On Tue, 05 Jun 2007 10:46:43 -0700
Mingming Cao <cmm@...ibm.com> wrote:
> The better choice to me is using ext4_blocks_count() to hide the details
> of the little endian. It's fine to use s_blocks_count_hi directly, just
> to make it clear, this is on-disk superblock data and better to do
> little endian conversion like read-in other on-disk superblock fields. 

On the grounds of avoiding confusion regarthing the use of
s_blocks_count_hi, I agree that using ext4_blocks_count() is the right
thing to do.  I will resubmit the patch and also eliminate the the 4
lines of comments since the code would be more explicit as to what its
doing.

> Yeah, it probably unnecessary in this case, but I don't think the extra
> instruction plays an important role in the performance, (this is only
> called at mount time, and there are lots of other places doing little
> endian conversion in ext4_fill_super() anyway).

I originally wrote this patch using ext4_blocks_count() but later
changed it since it was faster to do it this way.  While mounting is
not always a performance critical section, I still see those few extra
instructions a little wasteful. :)


-JRS
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