On Wed, Jan 27, 2016 at 02:35:04PM +0100, Vlastimil Babka wrote: > On 01/14/2016 06:24 AM, Joonsoo Kim wrote: > > In fact, I tested another idea implementing OBJFREELIST_SLAB with > > extendable linked array through another freed object. It can remove > > memory waste completely but it causes more computational overhead > > in critical lock path and it seems that overhead outweigh benefit. > > So, this patch doesn't include it. > > Can you elaborate? Do we actually need an extendable linked array? Why not just > store the pointer to the next free object into the object, NULL for the last > one? I.e. a singly-linked list. We should never need to actually traverse it? As Christoph explained, it's the way SLUB manages freed objects. In SLAB case, it doesn't want to touch object itself. It's one of main difference between SLAB and SLUB. These objects are cache-cold now so touching object itself could cause more cache footprint. > > freeing object obj: > *obj = page->freelist; > page->freelist = obj; > > allocating object: > obj = page->freelist; > page->freelist = *obj; > *obj = NULL; > > That means two writes, but if we omit managing page->active, it's not an It's not just matter of number of instructions as explained above. Touching more cache line should also be avoided. 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>