On 21.04.21 23:06, Eduardo Habkost wrote:
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>
Thanks Eduardo. I assume Paolo will be the right maintainer to pick this
up? (I hope he'll have time to look at this and some of my
pending-for-a-long-time series soon :( )
--
Thanks,
David / dhildenb
