On (Mon) 14 Jan 2013 [10:05:01], Luiz Capitulino wrote: > On Sat, 12 Jan 2013 02:13:17 +0530 > Amit Shah <amit.shah@xxxxxxxxxx> wrote: > > > On (Tue) 18 Dec 2012 [18:17:30], 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. > > > > > > This commit implements the guest side of auto-ballooning. > > > > > > To perform automatic deflate, the virtio_balloon driver registers > > > a shrinker callback, which will try to deflate the guest's balloon > > > on guest memory pressure just like if it were a cache. The shrinker > > > callback is only registered if the host supports the > > > VIRTIO_BALLOON_F_AUTO_BALLOON feature bit. > > > > I'm wondering if guest should auto-deflate even when the AUTO_BALLOON > > feature isn't supported by the host: if a guest is under pressure, > > there's no way for it to tell the host and wait for the host to > > deflate the balloon, so it may be beneficial to just go ahead and > > deflate the balloon for all hosts. > > I see two problems with this. First, this will automagically override > balloon changes done by the user; and second, if we don't have the > auto-inflate part and if the host starts facing memory pressure, VMs > may start getting OOM. Practically, though, at least for hosts and VMs managed by libvirt, guests will be confined by cgroups so they don't exceed some pre-defined quota. Guests should always be assumed to be malicious and / or greedy, so I'm certain all host mgmt software will have some checks in place. Amit -- 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>