On Tue, May 8, 2012 at 1:53 AM, Pekka Enberg <penberg@xxxxxxxxxx> wrote: > On Tue, May 8, 2012 at 8:42 AM, KOSAKI Motohiro > <kosaki.motohiro@xxxxxxxxx> wrote: >>> That said, I think you are being unfair to Anton who's one of the few >>> that's actually taking the time to implement this properly instead of >>> settling for an out-of-tree hack. >> >> Unfair? But only I can talk about technical comment. To be honest, I >> really dislike >> I need say the same explanation again and again. A lot of people don't read >> past discussion. And as far as the patches take the same mistake, I must say >> the same thing. It is just PITA. > > Unfair because you are trying to make it look as if Anton is only > concerned with his specific use case. That's simply not true. However current proposal certainly don't refer past discuss and don't work many environment. > On Tue, May 8, 2012 at 8:42 AM, KOSAKI Motohiro > <kosaki.motohiro@xxxxxxxxx> wrote: >> I don't disagree vmevent notification itself, but I must disagree lie >> notification. >> And also, To make just idea statistics doesn't make sense at all. How do an >> application choose the right events? If that depend on hardware configuration, >> userland developers can't write proper applications. > > That's exactly the problem we're trying to tackle here! We _want_ the > ABI to provide sane, well-defined events that solve real world > problems. Ok, sane. Then I take my time a little and review current vmevent code briefly. (I read vmevent/core branch in pekka's tree. please let me know if there is newer repositry) I think following thing should be fixed. 1) sample_period is brain damaged idea. If people ONLY need to sampling stastics, they only need to read /proc/vmstat periodically. just remove it and implement push notification. _IF_ someone need unfrequent level trigger, just use "usleep(timeout); read(vmevent_fd)" on userland code. 2) VMEVENT_ATTR_STATE_ONE_SHOT is misleading name. That is effect as edge trigger shot. not only once. 3) vmevent_fd() seems sane interface. but it has name space unaware. maybe we discuss how to harmonize name space feature. No hurry. but we have to think that issue since at beginning. 4) Currently, vmstat have per-cpu batch and vmstat updating makes 3 second delay at maximum. This is fine for usual case because almost userland watcher only read /proc/vmstat per second. But, for vmevent_fd() case, 3 seconds may be unacceptable delay. At worst, 128 batch x 4096 x 4k pagesize = 2G bytes inaccurate is there. 5) __VMEVENT_ATTR_STATE_VALUE_WAS_LT should be removed from userland exporting files. When exporing kenrel internal, always silly gus used them and made unhappy. 6) Also vmevent_event must hide from userland. 7) vmevent_config::size must be removed. In 20th century, M$ API prefer to use this technique. But They dropped the way because a lot of application don't initialize size member and they can't use it for keeping upper compitibility. 8) memcg unaware 9) numa unaware 10) zone unaware And, we may need vm internal change if we really need lowmem notification. current kernel don't have such info. _And_ there is one more big problem. Currently the kernel maintain memory per zone. But almost all userland application aren't aware zone nor node. Thus raw notification aren't useful for userland. In the other hands, total memory and total free memory is useful? Definitely No! Even though total free memory are lots, system may start swap out and oom invokation. If we can't oom invocation, this feature has serious raison d'etre issue. (i.e. (4), (8), (9) and (19) are not ignorable issue. I think) -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>