On 01/10/2018 18:24, Dave Hansen wrote: >> How should a policy in user space look like when new memory gets added >> - on s390x? Not onlining paravirtualized memory is very wrong. > > Because we're going to balloon it away in a moment anyway? No, rether somebody wanted this VM to have more memory, so it should use it - basically what HyperV or XEN also do. (in contrast to the concept of standby memory on s390). > > We have auto-onlining. Why isn't that being used on s390? Do you mean the sys parameter? How would that help? > > >> So the type of memory is very important here to have in user space. >> Relying on checks like "isS390()", "isKVMGuest()" or "isHyperVGuest()" >> to decide whether to online memory and how to online memory is wrong. >> Only some specific memory types (which I call "normal") are to be >> handled by user space. >> >> For the other ones, we exactly know what to do: >> - standby? don't online > > I think you're horribly conflating the software desire for what the stae > should be and the hardware itself. Agreed, user space should be able to configure it. > >>> As for the OOM issues, that sounds like something we need to fix by >>> refusing to do (or delaying) hot-add operations once we consume too much >>> ZONE_NORMAL from memmap[]s rather than trying to indirectly tell >>> userspace to hurry thing along. >> >> That is a moving target and doing that automatically is basically >> impossible. > > Nah. We know how much metadata we've allocated. We know how much > ZONE_NORMAL we are eating. We can *easily* add something to > add_memory() that just sleeps until the ratio is not out-of-whack. > >> You can add a lot of memory to the movable zone and >> everything is fine. Suddenly a lot of processes are started - boom. >> MOVABLE should only every be used if you expect an unplug. And for >> paravirtualized devices, a "typical" unplug does not exist. > > No, it's more complicated than that. People use MOVABLE, for instance, > to allow more consistent huge page allocations. It's certainly not just > hot-remove. > As noted in the other thread, that's a good point. We have to allow to make a decision in user space. I agree to your initial proposal to distinguish "standby" from "auto-online". It would allow to have sane defaults in user space. -- Thanks, David / dhildenb _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
