On Mon, Feb 27, 2017 at 04:43:04PM +0100, Michal Hocko wrote: > On Mon 27-02-17 12:25:10, Heiko Carstens wrote: > > On Mon, Feb 27, 2017 at 11:02:09AM +0100, Vitaly Kuznetsov wrote: > > > A couple of other thoughts: > > > 1) Having all newly added memory online ASAP is probably what people > > > want for all virtual machines. > > > > This is not true for s390. On s390 we have "standby" memory that a guest > > sees and potentially may use if it sets it online. Every guest that sets > > memory offline contributes to the hypervisor's standby memory pool, while > > onlining standby memory takes memory away from the standby pool. > > > > The use-case is that a system administrator in advance knows the maximum > > size a guest will ever have and also defines how much memory should be used > > at boot time. The difference is standby memory. > > > > Auto-onlining of standby memory is the last thing we want. > > > > > Unfortunately, we have additional complexity with memory zones > > > (ZONE_NORMAL, ZONE_MOVABLE) and in some cases manual intervention is > > > required. Especially, when further unplug is expected. > > > > This also is a reason why auto-onlining doesn't seem be the best way. > > Can you imagine any situation when somebody actually might want to have > this knob enabled? From what I understand it doesn't seem to be the > case. I can only speak for s390, and at least here I think auto-online is always wrong, especially if you consider the added complexity that you may want to online memory sometimes to ZONE_NORMAL and sometimes to ZONE_MOVABLE. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
