[PATCH] shrink_slab acounts for seeks incorrectly

wli points out that shrink_slab inverts the sense of shrinker->seeks: those
caches which require more seeks to reestablish an object are shrunk harder.
That's wrong - they should be shrunk less.

So fix that up, but scaling the result so that the patch is actually a no-op
at this time, because all caches use DEFAULT_SEEKS (2).

mm/vmscan.c

@@ -154,7 +154,7 @@ static int shrink_slab(long scanned, unsigned int gfp_mask)
 	list_for_each_entry(shrinker, &shrinker_list, list) {
 		unsigned long long delta;
 
-		delta = scanned * shrinker->seeks;
+		delta = 4 * (scanned / shrinker->seeks);
 		delta *= (*shrinker->shrinker)(0, gfp_mask);
 		do_div(delta, pages + 1);
 		shrinker->nr += delta;