On Tue, Mar 10, 2009 at 02:25:56PM -0400, Cole Robinson wrote: > Daniel P. Berrange wrote: > > This patch implements full support for memory ballooning in the QEMU > > driver. > > > > - Fix qemudBuildCommandLine() to set the initial boot time VM memory > > allocation based off the 'maxmem' config field. > > - Add call to 'qemudDomainSetMemoryBalloon' immediately at startup > > to make the guest balloon to initial requested allocation. > > - In the qemudDomainGetInfo() and qemudDomainDumpXML calls, query > > the monitor to find current balloon allocation and update config > > - Implement qemudDomainSetMemory() for running guests using the > > monitor balloon command > > > > In all of these scenarios, if the QEMU being used is too old to support > > the memory balloon device, the user will get a suitable error or it'll > > report the statically defined memory allocation from boot time. > > > > Before we balloon the guest at startup, does QEMU actually claim the > maxmem amount? As in, if maxmem is 4G, and mem is 512M, will qemu > starting grabbing the 4G in its first few moments?
Yes & no :-) QEMU/KVM doesn't actually pin all guest RAM in memory on startup. So if you boot a guest with maxmem=4G and memory=500 MB, even if the guest OS takes a while before loading the virtio_balloon.ko module, the guest won't be using all 4G of RAM. The host only pulls guest RAM into memory when pages are touched by the guest OS. > Also, if for some reason someone currently has different maxmem and mem > values for a QEMU/KVM version that doesn't support ballooning, their > guest will now use the maxmem amount? I don't think this is really a big > deal (since it's not very likely to happen), just curious. Yes, that is correct - it should have always been doing this because that's the same semantics that other drivers have. > > @@ -2473,8 +2572,15 @@ static int qemudDomainGetInfo(virDomainP > > } > > } > > > > + err = qemudDomainGetMemoryBalloon(dom->conn, vm, &balloon); > > + if (err < 0) > > + goto cleanup; > > + > > info->maxMem = vm->def->maxmem; > > - info->memory = vm->def->memory; > > + if (err == 0) /* Balloon not supported */ > > + info->memory = vm->def->memory; > > If balloon isn't supported, won't this always be maxmem, since that's > what we pass on the command line? That is true - we should probably set that explicitly to be clear. Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :| -- Libvir-list mailing list Libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
