On (Mon) 14 Jan 2013 [09:58:30], Luiz Capitulino wrote: > On Sat, 12 Jan 2013 02:02:32 +0530 > Amit Shah <amit.s...@redhat.com> wrote: > > > Hi Luiz, > > > > On (Tue) 18 Dec 2012 [18:16:55], Luiz Capitulino wrote: > > > The auto-ballooning feature automatically performs balloon inflate > > > or deflate based on host and guest memory pressure. This can help to > > > avoid swapping or worse in both, host and guest. > > > > > > Auto-ballooning has a host and a guest part. The host performs > > > automatic inflate by requesting the guest to inflate its balloon > > > when the host is facing memory pressure. The guest performs > > > automatic deflate when it's facing memory pressure itself. It's > > > expected that auto-inflate and auto-deflate will balance each > > > other over time. > > > > What does this last line mean? > > When qemu does auto-inflate, the guest memory will be reduced. Then it's > expected that something will increase it again. That something is > auto-deflate. > > However, if we deflate too much, than the host may face memory pressure, > and then auto-inflate will take place again. > > It's expected that that sequence of auto-inflate and auto-deflate will > reach a balance in some point in time.
This all depends on the loads on the systems and other external factors; we never know how things might behave. Let's just leave this line out. > > How about emitting a QMP message to notify > > management of auto-ballooning? > > I could think about that if they are interested. I think they would be - no harm in asking. > > > o this shouldn't override balloon changes done by the user manually > > > > Can you think of examples here? If the user (host admin) has > > ballooned an 8G guest down to 4G, auto-balloon will only further > > shrink down the guest RAM, so there's no real 'overriding' happening > > that I can think of. Of course, a guest can expand itself to, say, > > 5G, but that should be allowed as the guest might be under pressure. > > Yes, that's exactly my point above. I mean, taking your example, if > the user has ballooned an 8G down to 4G, should auto-balloon be allowed > to balloon to 5G or even back to 8G? I think it should be allowed by default, and tunable by user/management (i.e. qemu shouldn't create policy, but enforce one if provided). Amit