slab: Common constants for kmalloc boundaries

Standardize the constants that describe the smallest and largest
object kept in the kmalloc arrays for SLAB and SLUB.

Differentiate between the maximum size for which a slab cache is used
(KMALLOC_MAX_CACHE_SIZE) and the maximum allocatable size
(KMALLOC_MAX_SIZE, KMALLOC_MAX_ORDER).

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

1 files changed, 24 insertions, 10 deletions

diff --git a/include/linux/slab.h b/include/linux/slab.h
index c97fe92532d1..c01780540054 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -163,7 +163,12 @@ struct kmem_cache {
 #else /* CONFIG_SLOB */
 
 /*
- * The largest kmalloc size supported by the slab allocators is
+ * Kmalloc array related definitions
+ */
+
+#ifdef CONFIG_SLAB
+/*
+ * The largest kmalloc size supported by the SLAB allocators is
  * 32 megabyte (2^25) or the maximum allocatable page order if that is
  * less than 32 MB.
  *
@@ -173,9 +178,24 @@ struct kmem_cache {
  */
 #define KMALLOC_SHIFT_HIGH      ((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
                                 (MAX_ORDER + PAGE_SHIFT - 1) : 25)
+#define KMALLOC_SHIFT_MAX       KMALLOC_SHIFT_HIGH
+#define KMALLOC_SHIFT_LOW       5
+#else
+/*
+ * SLUB allocates up to order 2 pages directly and otherwise
+ * passes the request to the page allocator.
+ */
+#define KMALLOC_SHIFT_HIGH      (PAGE_SHIFT + 1)
+#define KMALLOC_SHIFT_MAX       (MAX_ORDER + PAGE_SHIFT)
+#define KMALLOC_SHIFT_LOW       3
+#endif
 
-#define KMALLOC_MAX_SIZE        (1UL << KMALLOC_SHIFT_HIGH)
-#define KMALLOC_MAX_ORDER       (KMALLOC_SHIFT_HIGH - PAGE_SHIFT)
+/* Maximum allocatable size */
+#define KMALLOC_MAX_SIZE        (1UL << KMALLOC_SHIFT_MAX)
+/* Maximum size for which we actually use a slab cache */
+#define KMALLOC_MAX_CACHE_SIZE  (1UL << KMALLOC_SHIFT_HIGH)
+/* Maximum order allocatable via the slab allocagtor */
+#define KMALLOC_MAX_ORDER       (KMALLOC_SHIFT_MAX - PAGE_SHIFT)
 
 /*
  * Kmalloc subsystem.
@@ -183,15 +203,9 @@ struct kmem_cache {
 #if defined(ARCH_DMA_MINALIGN) && ARCH_DMA_MINALIGN > 8
 #define KMALLOC_MIN_SIZE ARCH_DMA_MINALIGN
 #else
-#ifdef CONFIG_SLAB
-#define KMALLOC_MIN_SIZE 32
-#else
-#define KMALLOC_MIN_SIZE 8
-#endif
+#define KMALLOC_MIN_SIZE (1 << KMALLOC_SHIFT_LOW)
 #endif
 
-#define KMALLOC_SHIFT_LOW ilog2(KMALLOC_MIN_SIZE)
-
 /*
  * Figure out which kmalloc slab an allocation of a certain size
  * belongs to.