Re: dentry bloat.

[Andrew Morton <akpm@osdl.org>]

Maneesh Soni <maneesh@in.ibm.com> wrote:
>
> We can see this happening in the following numbers taken using dcachebench*
> gathered on 2-way P4 Xeon 2.4MHz SMP box with 4.5GB RAM. The benchmark was run
> with the following parameters and averaged over 10 runs.
> ./dcachebench -p 32 -b testdir
> 
> 		Average	microseconds/iterations 	Std. Deviation
> 		(lesser is better)
> 2.6.6		10204					161.5
> 2.6.6-mm1	10571					51.5
> 

Well..  this could be anything.  If the hash is any good -mm shouldn't be
doing significantly more locked operations.  (I think - didn't check very
closely).

Also the inode and dentry hash algorithms were changed in -mm.  You can
evaluate the effect of that by comparing 2.6.6 with current Linus -bk.

If we compare 2.6.6-bk with 2.6.6-mm1 and see a slowdown on SMP and no
slowdown on UP then yup, it might be due to additional locking.

But we should evaluate the hash changes separately.

Summary:

2.6.6-rc3:	baseline
2.6.6:		dentry size+alignment changes
2.6.6-bk: 	dentry size+alignment changes, hash changes
2.6.6-mm1:	dentry size+alignment changes, hash changes, lots of other stuff.