On Wed, Oct 02, 2013 at 10:02:12AM -0500, Eric Sandeen wrote:
> One thing I'm curious about - what changed from ext3 to ext4? I thought
> both defaulted to orlov and the same type of allocation behavior, more
> or less. I guess one change is that the "oldalloc" mount
> option went away.
Ext3 used an orlov style allocator as well. The main difference
between ext4 and ext3 is the orlov allocator is now done on a
per-flexbg basis instead of per-blockgroup basis.
That is, we do the statistics based on a flex-bg basis instead of the
blockgroup basis. As a result, I suspect Ben would see the inode
allocation behavior equivalent to ext3 if he creates the file system
using "mke2fs -t ext4 -G 1" to force the flex_bg size to 1.
Can you let me know what the size of the file system was, and mke2fs
parameters you were using for ext3 and ext4? I have a feeling that
inode allocations weren't optimal for your use case even with ext3,
but because we now spread the inodes based on flex_bg's instead of
block groups, that's why you saw the performance degredation.
- Ted
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