On Fri, Jun 28, 2013 at 03:44:02PM -0400, Luiz Capitulino wrote: > > Why can't you use poll() and demultiplex the events? Check if there is an > > event in the crit fd, and if there is, then just ignore all the rest. > > This may be a valid workaround for current kernels, but application > behavior will be different among kernels with a different number of > events. This is not a workaround, this is how poll works, and this is kinda expected... But not that I had this plan in mind when I was designing the current scheme... :) > Say, we events on top of critical. Then crit fd will now be > notified for cases where it didn't use to on older kernels. I'm not sure I am following here... but thinking about it more, I guess the extra read() will be needed anyway (to reset the counter). > > > However, it *is* possible to make non-strict work on strict if we make > > > strict default _and_ make reads on memory.pressure_level return > > > available events. Just do this on app initialization: > > > > > > for each event in memory.pressure_level; do > > > /* register eventfd to be notified on "event" */ > > > done > > > > This scheme registers "all" events. > > Yes, because I thought that's the user-case that matters for activity > manager :) Some activity managers use only low levels (Android), some might use only medium levels (simple load-balancing). Being able to register only "all" does not make sense to me. > > Here is more complicated case: > > > > Old kernels, pressure_level reads: > > > > low, med, crit > > > > The app just wants to listen for med level. > > > > New kernels, pressure_level reads: > > > > low, FOO, med, BAR, crit > > > > How would application decide which of FOO and BAR are ex-med levels? > > What you meant by ex-med? The scale is continuous and non-overlapping. If you add some other level, you effectively "shrinking" other levels, so the ex-med in the list above might correspond to "FOO, med" or "med, BAR" or "FOO, med, BAR", and that is exactly the problem. > Let's not over-design. I agree that allowing the API to be extended > is a good thing, but we shouldn't give complex meaning to events, > otherwise we're better with a numeric scale instead. I am not over-desiging at all. Again, you did not provide any solution for the case if we are going to add a new level. Thing is, I don't know if we are going to add more levels, but the three-levels scheme is not something scientifically proven, it is just an arbitrary thing we made up. We may end up with four, or five... or not. Thanks, Anton -- 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>