Patch from Andreas Gruenbacher <agruen@suse.de>

Add a gfp_mask parameter to the free() callback so that the callback can
safely do I/O, etc. The free callback can now also fail.  This will be
needed by reiserfs.

The order of entries on the cache entry lru is reversed so that
list_for_each_safe() can be used. Several helper functions that don't
make the code any better are removed. Finally, a couple of cosmetic
things.