Re: [libvirt] PATCH: Support memory ballooning for QEMU

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?

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.

> @@ -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?