On 05/03/2012 10:58 PM, Nitin Gupta wrote:
> On 5/3/12 2:40 AM, 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.
>
> Thanks,
> Nitin
>
>
>> if (!pool)
>> return NULL;
>>
>
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--
Kind regards,
Minchan Kim
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