[PATCH] slab: Bypass free lists for __drain_alien_cache()

__drain_alien_cache() currently drains objects by freeing them to the
(remote) freelists of the original node.  However, each node also has a
shared list containing objects to be used on any processor of that node.
We can avoid a number of remote node accesses by copying the pointers to
the free objects directly into the remote shared array.

And while we are at it: Skip alien draining if the alien cache spinlock is
already taken.

Kiran reported that this is a performance benefit.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>