Hello, On Tue, Aug 13, 2013 at 02:16:21PM -0700, Andrew Morton wrote: > I've yet to see any evidence that callback APIs have been abused and > I've yet to see any reasoning which makes me believe that this one will > be abused. Well, off the top of my head. * In general, it's clunkier. Callbacks become artificial boundaries across which context has to be carried over explicitly. It often involves packing data into a temporary struct. The artificial barrier also generally makes the logic more difficult to follow. This is pretty general problem with callback based interface and why many programming languages / conventions prefer iterator style interface over callback based ones. It makes the code a lot easier to organize around the looping construct. Here, it isn't as pronounced because the thing naturally requires a callback anyway. * From the API itself, it often isn't clear what restrictions the context the callback is called under would have. It sure is partly documentation problem but is pretty easy to get wrong inadvertantly as the code evolves and can be difficult to spot as the context isn't apparent. Moving away from callbacks started with higher level languages but the kernel sure is on the boat too where possible. This one is muddier as the interface is async in nature but still it's at least partially applicable. > > It feels a bit silly to me to push the API > > that way when doing so doesn't even solve the allocation problem. > > It removes the need to perform a cpumask allocation in > lru_add_drain_all(). But that doesn't really solve anything, does it? > > It doesn't really buy us much while making the interface more complex. > > It's a superior interface. It is more flexible but at the same time clunkier. I wouldn't call it superior and the flexibility doesn't buy us much here. Thanks. -- tejun -- 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>