[ovirt-devel] VDSM faqemu default memory change

Dan Kenigsberg danken at redhat.com
Tue Jun 17 22:09:26 UTC 2014

On Tue, Jun 10, 2014 at 10:43:36AM -0400, Martin Polednik wrote:
> Hello
> I'm writing in order to propose a change to faqemu hook as indicated in [1],
> modifying the hook's default behavior:
> There are currently hardcoded x86_64 and PPC memory limits (20480 and 262144),
> this change would remove these implicit constraints and keep the memory unchanged.
> A new variable in configuration is introduced, fake_kvm_memory, which allows you
> to limit the memory for both these platforms to a value (or using unchanged memory
> by setting it to 0, which is default).
> This means that running faqemu without modification would consume up to 10x times
> memory using default VM memory memory size for x86_64 and unchanged for PPC.
> [1] http://gerrit.ovirt.org/#/c/28320/

Let me rephrase the warning: Now, faqemu runs a qemu with the tiniest
memory possible, that is unable to host any guest. This makes it
maintain its purpose of seeming like a VM yet taking the least amounts
possible of CPU and memory.

With the suggested patch, this changes. Unless explicitly setting
fake_kvm_memory=20480, each qemu process would consume the full amount
of memory allocated to it. Anybody using faqemu should be aware of the
proposed change and agree to it.

If the users are unhappy with this, I'd suggest Martin to have a fresh
and simpler new hook, that only change the domain type from "kvm" to
"qemu", with no configurables and no change of behavior. On a second
thought, I belive it would be better, as with a fully-operational
emulated guest, this is no loger a fake qemu, but just a slow one.


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