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

[Joel Becker]

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@xxxxxxxxxxxx
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