From: Manfred Spraul <manfred@colorfullife.com>
Reversing the patches that made all caches hw cacheline aligned had an
unintended side effect on the kmalloc caches: Before they had the
SLAB_HWCACHE_ALIGN flag set, now it's clear. This breaks one sgi driver -
it expects aligned caches. Additionally I think it's the right thing to
do: It costs virtually nothing (the caches are power-of-two sized) and
could reduce false sharing.
Additionally, the patch adds back the documentation for the
SLAB_HWCACHE_ALIGN flag.
Signed-Off: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/mm/slab.c | 14 ++++++++++----
1 files changed, 10 insertions(+), 4 deletions(-)
diff -puN mm/slab.c~hwcache-align-kmalloc-caches mm/slab.c
--- 25/mm/slab.c~hwcache-align-kmalloc-caches 2004-06-19 14:18:09.798900488 -0700
+++ 25-akpm/mm/slab.c 2004-06-19 14:18:09.804899576 -0700
@@ -129,6 +129,10 @@
#define ARCH_KMALLOC_MINALIGN 0
#endif
+#ifndef ARCH_KMALLOC_FLAGS
+#define ARCH_KMALLOC_FLAGS SLAB_HWCACHE_ALIGN
+#endif
+
/* Legal flag mask for kmem_cache_create(). */
#if DEBUG
# define CREATE_MASK (SLAB_DEBUG_INITIAL | SLAB_RED_ZONE | \
@@ -758,7 +762,7 @@ void __init kmem_cache_init(void)
* allow tighter packing of the smaller caches. */
sizes->cs_cachep = kmem_cache_create(names->name,
sizes->cs_size, ARCH_KMALLOC_MINALIGN,
- SLAB_PANIC, NULL, NULL);
+ (ARCH_KMALLOC_FLAGS | SLAB_PANIC), NULL, NULL);
/* Inc off-slab bufctl limit until the ceiling is hit. */
if (!(OFF_SLAB(sizes->cs_cachep))) {
@@ -768,7 +772,8 @@ void __init kmem_cache_init(void)
sizes->cs_dmacachep = kmem_cache_create(names->name_dma,
sizes->cs_size, ARCH_KMALLOC_MINALIGN,
- (SLAB_CACHE_DMA | SLAB_PANIC), NULL, NULL);
+ (ARCH_KMALLOC_FLAGS | SLAB_CACHE_DMA | SLAB_PANIC),
+ NULL, NULL);
sizes++;
names++;
@@ -1116,8 +1121,9 @@ static void slab_destroy (kmem_cache_t *
* %SLAB_NO_REAP - Don't automatically reap this cache when we're under
* memory pressure.
*
- * %SLAB_HWCACHE_ALIGN - This flag has no effect and will be removed soon.
- *
+ * %SLAB_HWCACHE_ALIGN - Align the objects in this cache to a hardware
+ * cacheline. This can be beneficial if you're counting cycles as closely
+ * as davem.
*/
kmem_cache_t *
kmem_cache_create (const char *name, size_t size, size_t align,
_