SLUB: direct pass through of page size or higher kmalloc requests

This gets rid of all kmalloc caches larger than page size.  A kmalloc
request larger than PAGE_SIZE > 2 is going to be passed through to the page
allocator.  This works both inline where we will call __get_free_pages
instead of kmem_cache_alloc and in __kmalloc.

kfree is modified to check if the object is in a slab page. If not then
the page is freed via the page allocator instead. Roughly similar to what
SLOB does.

Advantages:
- Reduces memory overhead for kmalloc array
- Large kmalloc operations are faster since they do not
  need to pass through the slab allocator to get to the
  page allocator.
- Performance increase of 10%-20% on alloc and 50% on free for
  PAGE_SIZEd allocations.
  SLUB must call page allocator for each alloc anyways since
  the higher order pages which that allowed avoiding the page alloc calls
  are not available in a reliable way anymore. So we are basically removing
  useless slab allocator overhead.
- Large kmallocs yields page aligned object which is what
  SLAB did. Bad things like using page sized kmalloc allocations to
  stand in for page allocate allocs can be transparently handled and are not
  distinguishable from page allocator uses.
- Checking for too large objects can be removed since
  it is done by the page allocator.

Drawbacks:
- No accounting for large kmalloc slab allocations anymore
- No debugging of large kmalloc slab allocations.

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>

1 files changed, 24 insertions, 33 deletions

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 74962077f632..3b361b2906bd 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -72,7 +72,7 @@ struct kmem_cache {
  * 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[KMALLOC_SHIFT_HIGH + 1];
+extern struct kmem_cache kmalloc_caches[PAGE_SHIFT];
 
 /*
  * Sorry that the following has to be that ugly but some versions of GCC
@@ -83,9 +83,6 @@ static __always_inline int kmalloc_index(size_t size)
         if (!size)
                 return 0;
 
-        if (size > KMALLOC_MAX_SIZE)
-                return -1;
-
         if (size <= KMALLOC_MIN_SIZE)
                 return KMALLOC_SHIFT_LOW;
 
@@ -102,6 +99,10 @@ static __always_inline int kmalloc_index(size_t size)
         if (size <=        512) return 9;
         if (size <=       1024) return 10;
         if (size <=   2 * 1024) return 11;
+/*
+ * The following is only needed to support architectures with a larger page
+ * size than 4k.
+ */
         if (size <=   4 * 1024) return 12;
         if (size <=   8 * 1024) return 13;
         if (size <=  16 * 1024) return 14;
@@ -109,13 +110,9 @@ static __always_inline int kmalloc_index(size_t size)
         if (size <=  64 * 1024) return 16;
         if (size <= 128 * 1024) return 17;
         if (size <= 256 * 1024) return 18;
-        if (size <=  512 * 1024) return 19;
+        if (size <= 512 * 1024) return 19;
         if (size <= 1024 * 1024) return 20;
         if (size <=  2 * 1024 * 1024) return 21;
-        if (size <=  4 * 1024 * 1024) return 22;
-        if (size <=  8 * 1024 * 1024) return 23;
-        if (size <= 16 * 1024 * 1024) return 24;
-        if (size <= 32 * 1024 * 1024) return 25;
         return -1;
 
 /*
@@ -140,19 +137,6 @@ static __always_inline struct kmem_cache *kmalloc_slab(size_t size)
         if (index == 0)
                 return NULL;
 
-        /*
-         * This function only gets expanded if __builtin_constant_p(size), so
-         * testing it here shouldn't be needed.  But some versions of gcc need
-         * help.
-         */
-        if (__builtin_constant_p(size) && index < 0) {
-                /*
-                 * Generate a link failure. Would be great if we could
-                 * do something to stop the compile here.
-                 */
-                extern void __kmalloc_size_too_large(void);
-                __kmalloc_size_too_large();
-        }
         return &kmalloc_caches[index];
 }
 
@@ -168,15 +152,21 @@ void *__kmalloc(size_t size, gfp_t flags);
 
 static __always_inline void *kmalloc(size_t size, gfp_t flags)
 {
-        if (__builtin_constant_p(size) && !(flags & SLUB_DMA)) {
-                struct kmem_cache *s = kmalloc_slab(size);
+        if (__builtin_constant_p(size)) {
+                if (size > PAGE_SIZE / 2)
+                        return (void *)__get_free_pages(flags | __GFP_COMP,
+                                                        get_order(size));
 
-                if (!s)
-                        return ZERO_SIZE_PTR;
+                if (!(flags & SLUB_DMA)) {
+                        struct kmem_cache *s = kmalloc_slab(size);
+
+                        if (!s)
+                                return ZERO_SIZE_PTR;
 
-                return kmem_cache_alloc(s, flags);
-        } else
-                return __kmalloc(size, flags);
+                        return kmem_cache_alloc(s, flags);
+                }
+        }
+        return __kmalloc(size, flags);
 }
 
 #ifdef CONFIG_NUMA
@@ -185,15 +175,16 @@ 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) && !(flags & SLUB_DMA)) {
-                struct kmem_cache *s = kmalloc_slab(size);
+        if (__builtin_constant_p(size) &&
+                size <= PAGE_SIZE / 2 && !(flags & SLUB_DMA)) {
+                        struct kmem_cache *s = kmalloc_slab(size);
 
                 if (!s)
                         return ZERO_SIZE_PTR;
 
                 return kmem_cache_alloc_node(s, flags, node);
-        } else
-                return __kmalloc_node(size, flags, node);
+        }
+        return __kmalloc_node(size, flags, node);
 }
 #endif