Il 13/06/2013 08:50, Eduardo Habkost ha scritto: > I believe an interface based on guest physical memory addresses is more > flexible (and even simpler!) than one that only allows binding of whole > virtual NUMA nodes.
And "-numa node" is already one, what about just adding "mem-path=/foo" or "host_node=NN" suboptions? Then "-mem-path /foo" would be a shortcut for "-numa node,mem-path=/foo". I even had patches to convert -numa to QemuOpts, I can dig them out if your interested. Paolo > (And I still don't understand why you are exposing QEMU virtual memory > addresses in the new command, if they are useless). > > >>> >>> >>>>> * The correspondence between guest physical address ranges and ranges >>>>> inside the mapped files (so external tools could set the policy on >>>>> those files instead of requiring QEMU to set it directly) >>>>> >>>>> I understand that your use case may require additional information and >>>>> additional interfaces. But if we provide the information above we will >>>>> allow external components set the policy on the hugetlbfs files before >>>>> we add new interfaces required for your use case. >>>> >>>> But the file backed memory is not good for the host which has many >>>> virtual machines, in this situation, we can't handle anon THP yet. >>> >>> I don't understand what you mean, here. What prevents someone from using >>> file-backed memory with multiple virtual machines? >> >> While if we use hugetlbfs backed memory, we should know how many virtual >> machines, >> how much memory each vm will use, then reserve these pages for them. And even >> should reserve more pages for external tools(numactl) to set memory polices. >> Even the memory reservation also has it's own memory policies. It's very hard >> to control it to what we want to set. > > Well, it's hard because we don't even have tools to help on that, yet. > > Anyway, I understand that you want to make it work with THP as well. But > if THP works with tmpfs (does it?), people then could use exactly the > same file-based mechanisms with tmpfs and keep THP working. > > (Right now I am doing some experiments to understand how the system > behaves when using numactl on hugetlbfs and tmpfs, before and after > getting the files mapped). > > >>> >>>> >>>> And as I mentioned, the cross numa node access performance regression >>>> is caused by pci-passthrough, it's a very long time bug, we should >>>> back port the host memory pinning patch to old QEMU to resolve this >>>> performance >>>> problem, too. >>> >>> If it's a regression, what's the last version of QEMU where the bug >>> wasn't present? >>> >> >> As QEMU doesn't support host memory binding, I think >> this was present since we support guest NUMA, and the pci-passthrough made >> it even worse. > > If the problem was always present, it is not a regression, is it? >
