SLUB: Introduce and use SLUB_MAX_SIZE and SLUB_PAGE_SHIFT constants

As a preparational patch to bump up page allocator pass-through threshold,
introduce two new constants SLUB_MAX_SIZE and SLUB_PAGE_SHIFT and convert
mm/slub.c to use them.

Reported-by: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Tested-by: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

2 files changed, 24 insertions, 11 deletions

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 2f5c16b1aacd..986e09dcfd8f 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -121,10 +121,23 @@ struct kmem_cache {
 #define KMALLOC_SHIFT_LOW ilog2(KMALLOC_MIN_SIZE)
 
 /*
+ * Maximum kmalloc object size handled by SLUB. Larger object allocations
+ * are passed through to the page allocator. The page allocator "fastpath"
+ * is relatively slow so we need this value sufficiently high so that
+ * performance critical objects are allocated through the SLUB fastpath.
+ *
+ * This should be dropped to PAGE_SIZE / 2 once the page allocator
+ * "fastpath" becomes competitive with the slab allocator fastpaths.
+ */
+#define SLUB_MAX_SIZE (PAGE_SIZE)
+
+#define SLUB_PAGE_SHIFT (PAGE_SHIFT + 1)
+
+/*
  * We keep the general caches in an array of slab caches that are used for
  * 2^x bytes of allocations.
  */
-extern struct kmem_cache kmalloc_caches[PAGE_SHIFT + 1];
+extern struct kmem_cache kmalloc_caches[SLUB_PAGE_SHIFT];
 
 /*
  * Sorry that the following has to be that ugly but some versions of GCC
@@ -212,7 +225,7 @@ static __always_inline void *kmalloc_large(size_t size, gfp_t flags)
 static __always_inline void *kmalloc(size_t size, gfp_t flags)
 {
         if (__builtin_constant_p(size)) {
-                if (size > PAGE_SIZE)
+                if (size > SLUB_MAX_SIZE)
                         return kmalloc_large(size, flags);
 
                 if (!(flags & SLUB_DMA)) {
@@ -234,7 +247,7 @@ void *kmem_cache_alloc_node(struct kmem_cache *, gfp_t flags, int node);
 static __always_inline void *kmalloc_node(size_t size, gfp_t flags, int node)
 {
         if (__builtin_constant_p(size) &&
-                size <= PAGE_SIZE && !(flags & SLUB_DMA)) {
+                size <= SLUB_MAX_SIZE && !(flags & SLUB_DMA)) {
                         struct kmem_cache *s = kmalloc_slab(size);
 
                 if (!s)
diff --git a/mm/slub.c b/mm/slub.c
index bdc9abb08a23..5a5e7f5bf799 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2475,7 +2475,7 @@ EXPORT_SYMBOL(kmem_cache_destroy);
  *              Kmalloc subsystem
  *******************************************************************/
 
-struct kmem_cache kmalloc_caches[PAGE_SHIFT + 1] __cacheline_aligned;
+struct kmem_cache kmalloc_caches[SLUB_PAGE_SHIFT] __cacheline_aligned;
 EXPORT_SYMBOL(kmalloc_caches);
 
 static int __init setup_slub_min_order(char *str)
@@ -2537,7 +2537,7 @@ panic:
 }
 
 #ifdef CONFIG_ZONE_DMA
-static struct kmem_cache *kmalloc_caches_dma[PAGE_SHIFT + 1];
+static struct kmem_cache *kmalloc_caches_dma[SLUB_PAGE_SHIFT];
 
 static void sysfs_add_func(struct work_struct *w)
 {
@@ -2658,7 +2658,7 @@ void *__kmalloc(size_t size, gfp_t flags)
 {
         struct kmem_cache *s;
 
-        if (unlikely(size > PAGE_SIZE))
+        if (unlikely(size > SLUB_MAX_SIZE))
                 return kmalloc_large(size, flags);
 
         s = get_slab(size, flags);
@@ -2686,7 +2686,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
 {
         struct kmem_cache *s;
 
-        if (unlikely(size > PAGE_SIZE))
+        if (unlikely(size > SLUB_MAX_SIZE))
                 return kmalloc_large_node(size, flags, node);
 
         s = get_slab(size, flags);
@@ -2985,7 +2985,7 @@ void __init kmem_cache_init(void)
                 caches++;
         }
 
-        for (i = KMALLOC_SHIFT_LOW; i <= PAGE_SHIFT; i++) {
+        for (i = KMALLOC_SHIFT_LOW; i < SLUB_PAGE_SHIFT; i++) {
                 create_kmalloc_cache(&kmalloc_caches[i],
                         "kmalloc", 1 << i, GFP_KERNEL);
                 caches++;
@@ -3022,7 +3022,7 @@ void __init kmem_cache_init(void)
         slab_state = UP;
 
         /* Provide the correct kmalloc names now that the caches are up */
-        for (i = KMALLOC_SHIFT_LOW; i <= PAGE_SHIFT; i++)
+        for (i = KMALLOC_SHIFT_LOW; i < SLUB_PAGE_SHIFT; i++)
                 kmalloc_caches[i]. name =
                         kasprintf(GFP_KERNEL, "kmalloc-%d", 1 << i);
 
@@ -3222,7 +3222,7 @@ void *__kmalloc_track_caller(size_t size, gfp_t gfpflags, unsigned long caller)
 {
         struct kmem_cache *s;
 
-        if (unlikely(size > PAGE_SIZE))
+        if (unlikely(size > SLUB_MAX_SIZE))
                 return kmalloc_large(size, gfpflags);
 
         s = get_slab(size, gfpflags);
@@ -3238,7 +3238,7 @@ void *__kmalloc_node_track_caller(size_t size, gfp_t gfpflags,
 {
         struct kmem_cache *s;
 
-        if (unlikely(size > PAGE_SIZE))
+        if (unlikely(size > SLUB_MAX_SIZE))
                 return kmalloc_large_node(size, gfpflags, node);
 
         s = get_slab(size, gfpflags);