Christoph Lameter a écrit :
> On Thu, 23 Oct 2008, Eric Dumazet wrote:
> 
>>> SLUB touches objects by default when allocating. And it does it 
>>> immediately in slab_alloc() in order to retrieve the pointer to the 
>>> next object. So there is no point of hinting there right now.
>>>
>>
>> Please note SLUB touches by reading object.
>>
>> prefetchw() gives a hint to cpu saying this cache line is going to be 
>> *modified*, even
>> if first access is a read. Some architectures can save some bus 
>> transactions, acquiring
>> the cache line in an exclusive way instead of shared one.
> 
> Most architectures actually can do that. Its probably worth to run some 
> tests with that. Conversion of a cacheline from shared to exclusive can 
> cost something.
> 

Please check following patch as a followup

[PATCH] slub: slab_alloc() can use prefetchw()

Most kmalloced() areas are initialized/written right after allocation.

prefetchw() gives a hint to cpu saying this cache line is going to be
*modified*, even if first access is a read.

Some architectures can save some bus transactions, acquiring
the cache line in an exclusive way instead of shared one.

Same optimization was done in 2005 on SLAB in commit 
34342e863c3143640c031760140d640a06c6a5f8 
([PATCH] mm/slab.c: prefetchw the start of new allocated objects)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>