On 5/7/12 3:41 AM, Pekka Enberg wrote:
On Fri, 4 May 2012, Minchan Kim wrote:
It's a overkill to align pool size with PAGE_SIZE to avoid
false-sharing. This patch aligns it with just cache line size.
Signed-off-by: Minchan Kim<minchan@xxxxxxxxxx>
---
drivers/staging/zsmalloc/zsmalloc-main.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c
b/drivers/staging/zsmalloc/zsmalloc-main.c
index 51074fa..3991b03 100644
--- a/drivers/staging/zsmalloc/zsmalloc-main.c
+++ b/drivers/staging/zsmalloc/zsmalloc-main.c
@@ -489,14 +489,14 @@ fail:
struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
{
- int i, error, ovhd_size;
+ int i, error;
struct zs_pool *pool;
if (!name)
return NULL;
- ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
- pool = kzalloc(ovhd_size, GFP_KERNEL);
+ pool = kzalloc(ALIGN(sizeof(*pool), cache_line_size()),
+ GFP_KERNEL);
a basic question:
Is rounding off allocation size to cache_line_size enough to ensure
that the object is cache-line-aligned? Isn't it possible that even
though the object size is multiple of cache-line, it may still not be
properly aligned and end up sharing cache line with some other
read-mostly object?
AFAIK, SLAB allocates object aligned cache-size so I think that problem cannot happen.
But needs double check.
Cced Pekka.
The kmalloc(size) function only gives you the following guarantees:
(1) The allocated object is _at least_ 'size' bytes.
(2) The returned pointer is aligned to ARCH_KMALLOC_MINALIGN.
Anything beyond that is implementation detail and probably will break if
you switch between SLAB/SLUB/SLOB.
Pekka
So, we can probably leave it as is (PAGE_SIZE aligned) or use
kmem_cache_create(...,SLAB_HWCACHE_ALIGN,...) for allocating 'struct
zs_pool's.
zcache can potentially create a lot of pools, so the latter will save
some memory.
Thanks,
Nitin
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>