ima: use of radix tree cache indexing == massive waste of memory?

[H. Peter Anvin]

On 10/18/2010 09:48 AM, Eric Paris wrote:
> 
> 1) IMA uses radix trees which end up wasting 500 bytes per inode because
> the key is too sparse.  I've got a patch which uses an rbtree instead
> I'm testing and will send along shortly.  I found it funny working on
> the patch to see that Documentation/rbtree.txt says "This differs from
> radix trees (which are used to efficiently store sparse arrays and thus
> use long integer indexes to insert/access/delete nodes)"  Which flys in
> the face of this report.
> 

Radix trees can efficiently store data associated with sparse keys *as
long as the keys are clustered*.  For random key distributions, they
perform horribly.

	-hpa