linux-ext4 - Re: What's cooking in e2fsprogs.git (topics)

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Date:	Wed, 23 Apr 2008 13:02:31 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Theodore Tso <tytso@....EDU>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: What's cooking in e2fsprogs.git (topics)

On Mon, Apr 21, 2008 at 12:41:44PM -0400, Theodore Tso wrote:
> 
> * ak/undo-mgr (Mon Aug 13 15:56:26 2007 +0530) 6 commits
>  - Add test cases for undoe2fs: u_undoe2fs_mke2fs and
>    u_undoe2fs_tune2fs
>  - Fix the resize inode test case
>  - tune2fs: Support for large inode migration.
>  - mke2fs: Add support for the undo I/O manager.
>  - Add undoe2fs command
>  - libext2fs: Add undo I/O manager
> 
> 	These patches have been *significantly* rototilled.
> 
> 	* The test cases weren't correctly setting and deleting the
> 	  test_name.ok and test_name.failed files
> 
> 	* mke2fs would bomb out with an incomprehensible error message
> 	  if run twice in a row, or if the user didn't have write access
> 	  to /var/lib/e2fsprogs (some users run mke2fs as a non-root
> 	  user!)
> 
> 	* the undoe2fs program was calling com_err and passing
> 	  in uninitialized retval values, and was otherwise confused
> 	  about how to do proper error handling, resulting in garbage
> 	  getting printed if the file passed in didn't exist
> 
> 	* there was a terrible performance problem because in the
> 	  mke2fs case, the undo manager was using a tdb_data_size of
> 	  512.
> 
> 	* I added the ability to configure the location of the scratch
>           dirctory via mke2fs.conf for mk2efs.  What we should do for
>           tune2fs is less clear, and still needs to be addressed.  It
>           is also possible to force an undo file to be always created,
>           and not just when doing a lazy inode table initialization.
>           By using a 4k instead of 512 tdb_data_size, the time to
>           speed up an mke2fs was cut in half, while still using an
>           undo file.  I suspect if we force the tdb_data_size to be
>           even larger, say 32k or 64k the overhead would shrink even
>           more.
> 
> 	Unfortunately, there appears to be some kind of data
> 	corruption bug if I force a tdb_data_size of 32768, so I'm not
> 	entirely sure I trust the undo manager to be working
> 	correctly.  The undo_manager code itself needs a pretty
> 	serious auditing and checking to make sure it's doing the
> 	right thing with large tdb_data_sizes.
> 

undo-mgr is using the first blocks size used to write. This was done as
per the discussion at

http://thread.gmane.org/gmane.comp.file-systems.ext4/1942
http://thread.gmane.org/gmane.comp.file-systems.ext4/2056

I am not sure how you are forcing larger tdb_data_size. Can you send me
the changes so that I can test it and see what is wrong.

-aneesh

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