SLUB: extract dma_kmalloc_cache from get_cache.

The rarely used dma functionality in get_slab() makes the function too
complex.  The compiler begins to spill variables from the working set onto the
stack.  The created function is only used in extremely rare cases so make sure
that the compiler does not decide on its own to merge it back into get_slab().
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -2272,19 +2272,9 @@ static struct kmem_cache *create_kmalloc_cache(struct kmem_cache *s,
 	panic("Creation of kmalloc slab %s size=%d failed.\n", name, size);
 }
 
-static struct kmem_cache *get_slab(size_t size, gfp_t flags)
-{
-	int index = kmalloc_index(size);
-
-	if (!index)
-		return ZERO_SIZE_PTR;
-
-	/* Allocation too large? */
-	if (index < 0)
-		return NULL;
-
 #ifdef CONFIG_ZONE_DMA
-	if ((flags & SLUB_DMA)) {
+static noinline struct kmem_cache *dma_kmalloc_cache(int index, gfp_t flags)
+{
 	struct kmem_cache *s;
 	struct kmem_cache *x;
 	char *text;
@@ -2313,7 +2303,23 @@ static struct kmem_cache *get_slab(size_t size, gfp_t flags)
 	s = create_kmalloc_cache(x, text, realsize, flags);
 	kmalloc_caches_dma[index] = s;
 	return s;
-	}
+}
+#endif
+
+static struct kmem_cache *get_slab(size_t size, gfp_t flags)
+{
+	int index = kmalloc_index(size);
+
+	if (!index)
+		return ZERO_SIZE_PTR;
+
+	/* Allocation too large? */
+	if (index < 0)
+		return NULL;
+
+#ifdef CONFIG_ZONE_DMA
+	if ((flags & SLUB_DMA))
+		return dma_kmalloc_cache(index, flags);
 #endif
 	return &kmalloc_caches[index];
 }