On Thu, Aug 22, 2013 at 04:47:25PM +0000, Christoph Lameter wrote: > On Thu, 22 Aug 2013, Joonsoo Kim wrote: > > > And this patchset change a management method of free objects of a slab. > > Current free objects management method of the slab is weird, because > > it touch random position of the array of kmem_bufctl_t when we try to > > get free object. See following example. > > The ordering is intentional so that the most cache hot objects are removed > first. Yes, I know. > > > To get free objects, we access this array with following pattern. > > 6 -> 3 -> 7 -> 2 -> 5 -> 4 -> 0 -> 1 -> END > > Because that is the inverse order of the objects being freed. > > The cache hot effect may not be that significant since per cpu and per > node queues have been aded on top. So maybe we do not be so cache aware > anymore when actually touching struct slab. I don't change the ordering, I just change how we store that order to reduce cache footprint. We can simply implement this order via stack. Assume indexes of free order are 1 -> 0 -> 4. Currently, this order is stored in very complex way like below. struct slab's free = 4 kmem_bufctl_t array: 1 END ACTIVE ACTIVE 0 If we allocate one object, we access slab's free and index 4 of kmem_bufctl_t array. struct slab's free = 0 kmem_bufctl_t array: 1 END ACTIVE ACTIVE ACTIVE <we get object at index 4> And then, struct slab's free = 1 kmem_bufctl_t array: ACTIVE END ACTIVE ACTIVE ACTIVE <we get object at index 0> And then, struct slab's free = END kmem_bufctl_t array: ACTIVE ACTIVE ACTIVE ACTIVE ACTIVE <we get object at index 0> Following is newly implementation (stack) in same situation. struct slab's free = 0 kmem_bufctl_t array: 4 0 1 To get an one object, struct slab's free = 1 kmem_bufctl_t array: dummy 0 1 <we get object at index 4> And then, struct slab's free = 2 kmem_bufctl_t array: dummy dummy 1 <we get object at index 0> struct slab's free = 3 kmem_bufctl_t array: dummy dummy dummy <we get object at index 1> The order of returned object is same as previous algorithm. However this algorithm sequentially accesses kmem_bufctl_t array, instead of randomly access. This is an advantage of this patch. Thanks. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>