On Mon 07-04-14 09:40:28, Andi Kleen wrote: > Jan Kara <jack@xxxxxxx> writes: > > > > What we really need is a counter where we can better estimate counts > > accumulated in the percpu part of it. As the counter approaches zero, it's > > CPU overhead will have to become that of a single locked variable but when > > the value of counter is relatively high, we want it to be fast as the > > percpu one. Possibly, each CPU could "reserve" part of the value in the > > counter (by just decrementing the total value; how large that part should > > be really needs to depend to the total value of the counter and number of > > CPUs - in this regard we really differ from classical percpu couters) and > > allocate/free using that part. If CPU cannot reserve what it is asked for > > anymore, it would go and steal from parts other CPUs have accumulated, > > returning them to global pool until it can satisfy the allocation. > > That's a percpu_counter() isn't it? (or cookie jar) Not quite. We could use __percpu_counter_add() to set batch size for each operation depending on the current counter value. But still we don't want any cpu-local count to go negative (as then we cannot rely on global counter to give us a lower bound on number of free blocks). Also stealing from different cpu needs to be implemented... > The MM uses similar techniques. Where exactly? I'd be happy to be inspired :). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
