On Wed, Apr 21, 2021 at 02:26:09PM +0200, David Hildenbrand wrote: > Based-on: 20210406080126.24010-1-da...@redhat.com > > Some cleanups previously sent in other context (resizeable allocations), > followed by RAM_NORESERVE, implementing it under Linux using MAP_NORESERVE, > and letting users configure it for memory backens using the "reserve" > property (default: true). > > MAP_NORESERVE under Linux has in the context of QEMU an effect on > 1) Private/shared anonymous memory > -> memory-backend-ram,id=mem0,size=10G > 2) Private fd-based mappings > -> memory-backend-file,id=mem0,size=10G,mem-path=/dev/shm/0 > -> memory-backend-memfd,id=mem0,size=10G > 3) Private/shared hugetlb mappings > -> memory-backend-memfd,id=mem0,size=10G,hugetlb=on,hugetlbsize=2M > > With MAP_NORESERVE/"reserve=off", we won't be reserving swap space (1/2) or > huge pages (3) for the whole memory region. > > The target use case is virtio-mem, which dynamically exposes memory > inside a large, sparse memory area to the VM. MAP_NORESERVE tells the OS > "this mapping might be very sparse". This essentially allows > avoiding having to set "/proc/sys/vm/overcommit_memory == 1") when using > virtio-mem and also supporting hugetlbfs in the future.
For the memory backend and machine core code: Acked-by: Eduardo Habkost <ehabk...@redhat.com> -- Eduardo
