On Fri, 28 Jun 2013 11:45:47 -0700 Anton Vorontsov <anton@xxxxxxxxxx> wrote: > On Fri, Jun 28, 2013 at 02:25:58PM -0400, Luiz Capitulino wrote: > > > > > That's how it's expected to work, because on strict mode you're notified > > > > > for the level you registered for. So apps registering for critical, will > > > > > still be notified on critical just like before. > > > > > > > > Suppose you introduce a new level, and the system hits this level. Before, > > > > the app would receive at least some notification for the given memory load > > > > (i.e. one of the old levels), with the new level introduced in the kernel, > > > > the app will receive no events at all. > > > > That's not true. If an app registered for critical it will still get > > critical notification when the system is at the critical level. Just as it > > always did. No new events will change this. > > > > With today's semantics though, new events will change when current events > > are triggered. So each new extension will cause applications to have > > different behaviors, in different kernel versions. This looks quite > > undesirable to me. > > I'll try to explain it again. > > Old behaviour: > > low -> event > x <- but the system is at this unnamed level, between low and med > med > crit > > > We add a level: > > low > low-med <- system at this state, we send an event, but the old app does > not know about it, so it won't receive *any* notifications. (In > older kernels it would receive low level notification > med > crit > > You really don't see a problem here? I do get what you're saying. We disagree it's a problem. In my mind the best API is to get what you registered for. Nothing more, nothing less. Now, there might be ways around it (being it a problem or not). I was also considering this: > 3. Never change the levels (how can we know?) If we fail at determining levels (I honestly think current levels are all we need), we can add a new interface later. Also, what I said in the last email should work, which is to make memory.pressure_level return supported levels, so an application can register for all available levels. This way it will never miss a level. I also think this matches having the mechanism in the kernel and policy in user-space. -- 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>