On Tue, Feb 17, 2015 at 11:59:48AM +0100, Paolo Bonzini wrote: > > > On 17/02/2015 10:02, Michael S. Tsirkin wrote: > > > Increasing VHOST_MEMORY_MAX_NREGIONS from 65 to 509 > > > to match KVM_USER_MEM_SLOTS fixes issue for vhost-net. > > > > > > Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx> > > > > This scares me a bit: each region is 32byte, we are talking > > a 16K allocation that userspace can trigger. > > What's bad with a 16K allocation? It fails when memory is fragmented. > > How does kvm handle this issue? > > It doesn't. > > Paolo I'm guessing kvm doesn't do memory scans on data path, vhost does. qemu is just doing things that kernel didn't expect it to need. Instead, I suggest reducing number of GPA<->HVA mappings: you have GPA 1,5,7 map them at HVA 11,15,17 then you can have 1 slot: 1->11 To avoid libc reusing the memory holes, reserve them with MAP_NORESERVE or something like this. We can discuss smarter lookup algorithms but I'd rather userspace didn't do things that we then have to work around in kernel. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
