linux-ext4 - Re: [PATCH 0/2] Add inode checksum support to ext4

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Message-ID: <20110729131937.GB5910@noexit.corp.google.com>
Date:	Fri, 29 Jul 2011 06:19:38 -0700
From:	Joel Becker <jlbec@...lplan.org>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
Cc:	"Darrick J. Wong" <djwong@...ibm.com>,
	Andreas Dilger <aedilger@...il.com>,
	Mingming Cao <cmm@...ibm.com>, Theodore Ts'o <tytso@....edu>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Add inode checksum support to ext4

On Fri, Jul 29, 2011 at 03:48:45AM -0600, Andreas Dilger wrote:
> On 2011-07-28, at 4:07 PM, Joel Becker wrote:
> > 	We use ethernet crc32 in ocfs2.  btrfs uses crc32c.  Frankly, I
> > could have used crc32c if I'd really thought about the hardware
> > acceleration benefits.  I think it's a good idea for ext4.
> 
> The problem with crc32[c] is that if you don't have hardware acceleration
> it is terribly slow.

	We find ethernet crc32 just fine in ocfs2.  I use the kernel's
implementation, which survives everyone's network traffic, and of course
we added the triggers to jbd2 so we only have to do the calculations on
read and write.

> Yes, it makes sense to just put a "fake" dirent at the end of the leaf block,
> or similar.  I don't think it is necessary to modify existing directories or
> extent blocks to add these structures in, if there is no room, but for new
> blocks, or blocks with space it is enough.

	We have tunefs.ocfs2 code to adjust existing directories to add
the trailer.  It's not too bad, really.
 
Joel

-- 

"People with narrow minds usually have broad tongues."

			http://www.jlbec.org/
			jlbec@...lplan.org
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