On 12/9/24 4:01 PM, David Hildenbrand wrote: > On 09.12.24 20:29, Matthew Rosato wrote: > > Hi, > > Trying to wrap my head around that ... you mention that "pin the entirety of > guest memory". > > Do you mean that we will actually end up longterm pinning all guest RAM in > the kernel, similar to what vfio ends up doing?
Yes. Actually, the usecase here is specifically PCI passthrough via vfio-pci on s390. Unlike other platforms, the default s390 approach only pins on-demand and doesn't longterm pin all guest RAM, which is nice from a memory footprint perspective but pays a price via all those guest-2 RPCIT instructions. The goal here is now provide the optional alternative to longterm pin like other platforms. > > In that case, it would be incompatible with virtio-balloon (and without > modifications with upcoming virtio-mem). Is there already a mechanism in > place to handle that -- a call to ram_block_discard_disable() -- or even a > way to support coordinated discarding of RAM (e.g., virtio-mem + vfio)? Good point, should be calling add ram_block_discard_disable(true) when set register + a corresponding (false) during deregister... Will add for v2. As for supporting coordinated discard, I was hoping to subsequently look at virtio-mem for this. Thanks, Matt
