Re: large fs testing

[Theodore Tso <tytso@mit.edu>]

On Tue, May 26, 2009 at 03:21:32PM -0600, Andreas Dilger wrote:
> On May 26, 2009  13:47 -0400, Ric Wheeler wrote:
> > These runs were without lazy init, so I would expect to be a little more 
> > than twice as slow as your second run (not the three times I saw) 
> > assuming that it scales linearly.
> 
> Making lazy_itable_init the default formatting option for ext4 is/was
> dependent upon the kernel doing the zeroing of the inode table blocks
> at first mount time.  I'm not sure if that was implemented yet.

No, it hasn't been implemented yet.  If someone would like to step
forward, it's not hard patch to write.  The good news is that there's
no need to actually use the journal for most of the zero'ing;
basically, the design would be for each block group, if the inode
table hasn't been initialized, to call write_down on the per-block
group alloc_sem semphaore in ext4_group_info, initialize the inode
table in the unused portion of the block group (which can be calucated
from ext4_itable_unused_count()), then release the alloc_sem
semaphore, and then (under journal protection) set the
EXT4_BG_INODE_ZEROED flag in the block group descriptor.

If someone hurries, we could get this done before the next merge
window opens (probably in a week or two).

						- Ted