On Mon, Jul 13, 2015 at 08:55:13PM +0200, Igor Mammedov wrote: > On Mon, 13 Jul 2015 09:55:18 +0300 > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > On Fri, Jul 10, 2015 at 12:12:36PM +0200, Igor Mammedov wrote: > > > On Thu, 9 Jul 2015 16:46:43 +0300 > > > "Michael S. Tsirkin" <m...@redhat.com> wrote: > > > > > > > On Thu, Jul 09, 2015 at 03:43:01PM +0200, Paolo Bonzini wrote: > > > > > > > > > > > > > > > On 09/07/2015 15:06, Michael S. Tsirkin wrote: > > > > > > > QEMU asserts in vhost due to hitting vhost backend limit > > > > > > > on number of supported memory regions. > > > > > > > > > > > > > > Describe all hotplugged memory as one continuos range > > > > > > > to vhost with linear 1:1 HVA->GPA mapping in backend. > > > > > > > > > > > > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > > > > > > > > > > > > Hmm - a bunch of work here to recombine MRs that memory > > > > > > listener interface breaks up. In particular KVM could > > > > > > benefit from this too (on workloads that change the table a > > > > > > lot). Can't we teach memory core to pass hva range as a > > > > > > single continuous range to memory listeners? > > > > > > > > > > Memory listeners are based on memory regions, not HVA ranges. > > > > > > > > > > Paolo > > > > > > > > Many listeners care about HVA ranges. I know KVM and vhost do. > > > I'm not sure about KVM, it works just fine with fragmented memory > > > regions, the same will apply to vhost once module parameter to > > > increase limit is merged. > > > > > > but changing generic memory listener interface to replace HVA mapped > > > regions with HVA container would lead to a case when listeners > > > won't see exact layout that they might need. > > > > I don't think they care, really. > > > > > In addition vhost itself will suffer from working with big HVA > > > since it allocates log depending on size of memory => bigger log. > > > > Not really - it allocates the log depending on the PA range. > > Leaving unused holes doesn't reduce it's size. > if it would use HVA container instead then it will always allocate > log for max possible GPA, meaning that -m 1024,maxmem=1T will waste > a lot of memory and more so for bigger maxmem. > It's still possible to induce worst case by plugging pc-dimm at the end > of hotplug-memory area by specifying address for it explicitly. > That problem exists since memory hot-add was introduced, I've just > haven't noticed it back then.
There you are then. Depending on maxmem seems cleaner as it's more predictable. > It's perfectly fine to allocate log by last GPA as far as > memory is nearly continuous but memory hot-add makes it possible to > have sparse layout with a huge gaps between guest mapped RAM > which makes current log handling inefficient. > > I wonder how hard it would be to make log_size depend on present RAM > size rather than max present GPA so it wouldn't allocate excess > memory for log. We can simply map the unused parts of the log RESERVED. That can be a natural continuation of these series, but I don't think it needs to block it. > > > > > > > > That's one of the reasons that in this patch HVA ranges in > > > memory map are compacted only for backend consumption, > > > QEMU's side of vhost uses exact map for internal purposes. > > > And the other reason is I don't know vhost enough to rewrite it > > > to use big HVA for everything. > > > > > > > I guess we could create dummy MRs to fill in the holes left by > > > > memory hotplug? > > > it looks like nice thing from vhost pov but complicates other side, > > > > What other side do you have in mind? > > > > > hence I dislike an idea inventing dummy MRs for vhost's convenience. > memory core, but lets see what Paolo thinks about it. > > > > > > > > > > > vhost already has logic to recombine > > > > consequitive chunks created by memory core. > > > which looks a bit complicated and I was thinking about simplifying > > > it some time in the future. > >
