On Tue, 13 Aug 2013 18:33:04 -0400 Tejun Heo <tj@xxxxxxxxxx> wrote: > Hello, Andrew. > > On Tue, Aug 13, 2013 at 03:18:05PM -0700, Andrew Morton wrote: > > I don't buy it. The callback simply determines whether "we need to > > schuedule work on this cpu". It's utterly simple. Nobody will have > > trouble understanding or using such a thing. > > Well, I don't buy that either. Callback based interface has its > issues. No it hasn't. It's a common and simple technique which we all understand. > The difference we're talking about here is pretty minute but > then again the improvement brought on by the callback is pretty minute > too. It's a relatively small improvement in the lru_add_drain_all() case. Other callsites can gain improvements as well. > > It removes one memory allocation and initialisation per call. It > > removes an entire for_each_online_cpu() loop. > > But that doesn't solve the original problem at all and while it > removes the loop, it also adds a separate function. It results in superior runtime code. At this and potentially other callsites. > > I really don't understand what's going on here. You're advocating for > > a weaker kernel interface and for inferior kernel runtime behaviour. > > Forcing callers to communicate their needs via a large, > > dynamically-allocated temporary rather than directly. And what do we > > get in return for all this? Some stuff about callbacks which frankly > > has me scratching my head. > > Well, it is a fairly heavy path and you're pushing for an optimization > which won't make any noticeable difference at all. And, yes, I do > think we need to stick to simpler APIs whereever possible. Sure the > difference is minute here but the addition of test callback doesn't > buy us anything either, so what's the point? It does buy us things, as I've repeatedly described. You keep on saying things which demonstrably aren't so. I think I'll give up now. -- 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>