slab: clarify and fix calculate_slab_order()

If we triggered the 'offslab_limit' test, we would return with
cachep->gfporder incremented once too many times.

This clarifies the logic somewhat, and fixes that bug.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/slab.c b/mm/slab.c
index 2b0b1519bb74f472cb8894d823c93763ace80b26..f2e92dc1c9ce3d1fe1ca8cdfe685684f5bc1005d 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1628,36 +1628,36 @@ static inline size_t calculate_slab_order(struct kmem_cache *cachep,
                        size_t size, size_t align, unsigned long flags)
 {
        size_t left_over = 0;
+       int gfporder;
 
-       for (;; cachep->gfporder++) {
+       for (gfporder = 0 ; gfporder <= MAX_GFP_ORDER; gfporder++) {
                unsigned int num;
                size_t remainder;
 
-               if (cachep->gfporder > MAX_GFP_ORDER) {
-                       cachep->num = 0;
-                       break;
-               }
-
-               cache_estimate(cachep->gfporder, size, align, flags,
-                              &remainder, &num);
+               cache_estimate(gfporder, size, align, flags, &remainder, &num);
                if (!num)
                        continue;
+
                /* More than offslab_limit objects will cause problems */
-               if (flags & CFLGS_OFF_SLAB && cachep->num > offslab_limit)
+               if ((flags & CFLGS_OFF_SLAB) && num > offslab_limit)
                        break;
 
+               /* Found something acceptable - save it away */
                cachep->num = num;
+               cachep->gfporder = gfporder;
                left_over = remainder;
 
                /*
                 * Large number of objects is good, but very large slabs are
                 * currently bad for the gfp()s.
                 */
-               if (cachep->gfporder >= slab_break_gfp_order)
+               if (gfporder >= slab_break_gfp_order)
                        break;
 
-               if ((left_over * 8) <= (PAGE_SIZE << cachep->gfporder))
-                       /* Acceptable internal fragmentation */
+               /*
+                * Acceptable internal fragmentation?
+                */
+               if ((left_over * 8) <= (PAGE_SIZE << gfporder))
                        break;
        }
        return left_over;