On Sat, 23 Jun 2012, Joonsoo Kim wrote: > In some case of __slab_free(), we need a lock for manipulating partial list. > If freeing object with a lock is failed, a lock doesn't needed anymore > for some reasons. > > Case 1. prior is NULL, kmem_cache_debug(s) is true > > In this case, another free is occured before our free is succeed. > When slab is full(prior is NULL), only possible operation is slab_free(). > So in this case, we guess another free is occured. > It may make a slab frozen, so lock is not needed anymore. A free cannot freeze the slab without taking the lock. The taken lock makes sure that the thread that first enters slab_free() will be able to hold back the thread that wants to freeze the slab. > Case 2. inuse is NULL > > In this case, acquire_slab() is occured before out free is succeed. > We have a last object for slab, so other operation for this slab is > not possible except acquire_slab(). > Acquire_slab() makes a slab frozen, so lock is not needed anymore. acquire_slab() also requires lock acquisition and would be held of by slab_free holding the lock. > This also make logic somehow simple that 'was_frozen with a lock' case > is never occured. Remove it. That is actually interesting and would be a good optimization. -- 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>