Re: delalloc is crippling fs_mark performance

[Eric Sandeen <sandeen@redhat.com>]

Eric Sandeen wrote:
> running fs_mark like this:
> 
> fs_mark -d /mnt/test -D 256 -n 100000 -t 4 -s 20480 -F -S 0
> 
> (256 subdirs, 100000 files/iteration, 4 threads, 20k files, no sync)
> 
> on a 1T fs, with and without delalloc (mount option), is pretty interesting:
> 
> http://people.redhat.com/esandeen/ext4/fs_mark.png

I've updated this graph with another run where the group_prealloc
tuneable was set to a perfect multiple of the allocation size, or 500
blocks.  This way the leftover 2-block preallocations don't wind up
causing the list to grow with unuseable tiny leftover preallocations.
After tuning this way, it does clearly seem to be the problem here.

-Eric