On Wed, Dec 11, 2013 at 03:45:29PM +0100, Paolo Bonzini wrote: > Il 11/12/2013 15:20, Michael S. Tsirkin ha scritto: > > > It means that its necessary to expose that 3-4GB physical memory region > > > in QEMU belongs to the same node (that is, guest must be aware that > > > 3-3.75GB and the tail of RAM are on the same node). > > > > > > So the problem Paolo mentions is fixable. > > I'm not sure if it is fixable. You need a 2M mountpoint to bind the 3G-4G > range correctly, a 1G mountpoint for everything else, and QEMU only allows > to specify one path. > > Without Marcelo's patch there is a workaround; if you know the size of the 4G > hole and configure the first two nodes with unequal sizes. For example > > -m 8192 \ > -object memory-ram,id=ram-node0,size=3840M,hostnode=0 -numa > node,memdev=ram-node0 \ > -object memory-ram,id=ram-node1,size=4352M,hostnode=1 -numa > node,memdev=ram-node1 > > RAM address Host virtual address low bits Guest physical > addresses > 0M-3840M 0 0M-3840M > 3840M-8192M 0 4096M-8448M > > Then you'll waste 1GB of RAM (you'll use 9 hugepages instead of 8), but > everything will be aligned. Or you just make your guest 7680M and not waste > the memory. > > But with Marcelo's patch, ram-node1 will be split in two. QEMU will try > to realign the second part of ram-node1, but the result is that the second > part is misaligned and only the first 256M (the tail of guest physical > memory) stays aligned: > > RAM address Host virtual address low bits Guest physical > addresses > 0M-3840M 0 0M-3840M > 4096M-8192M 256M 4096M-8192M > 3840M-4096M 0 8192M-8448M > > So you still waste memory, _and_ get incorrect alignment. > > > Okay so > > Marcelo - do you ack this patch for 2.0? > > Paolo - do you re-ack this patch for 2.0? > > I very much prefer Gerd's approach.
Thanks, I will drop this from my tree for now. Please re-submit if you reconsider. > 2GB low memory for q35 is a bit wasteful, > but we have some time to fix that before release. > > Paolo How would you fix that? -- MST
