Some fixes for shared anonymous memory, cleanups previously sent in other
context (resizeable allocations), followed by RAM_NORESERVE, implementing
it under POSIX 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.
virtio-mem currently only supports anonymous memory, in the future we want
to also support private memfd, shared file-based and shared hugetlbfs
mappings.
virtio-mem features I am currently working on that will make it all
play together with this work include:
1. Introducing a prealloc option for virtio-mem (e.g., using fallocate()
when plugging blocks) to fail nicely when running out of
backing storage like huge pages ("prealloc=on").
2. Handling virtio-mem requests via an iothread to not hold the BQL while
populating/preallocating memory ("iothread=X").
3. Protecting unplugged memory e.g., using userfaultfd ("prot=uffd").
4. Dynamic reservation of swap space ("reserve=on")
5. Supporting resizable RAM block/memmory regions, such that we won't
always expose a large, sparse memory region to the VM.
6. (resizeable allocations / optimized mmap handling when resizing RAM
blocks)
Based-on: 20210303130916.22553-1-da...@redhat.com
v2 -> v3:
- Renamed "softmmu/physmem: Drop "shared" parameter from ram_block_add()"
to "softmmu/physmem: Mark shared anonymous memory RAM_SHARED" and
adjusted the description
- Added "softmmu/physmem: Fix ram_block_discard_range() to handle shared
anonymous memory"
- Added "softmmu/physmem: Fix qemu_ram_remap() to handle shared anonymous
memory"
- Added "util/mmap-alloc: Pass flags instead of separate bools to
qemu_ram_mmap()"
- "util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE"
-- Further tweak code comments
-- Handle shared anonymous memory
v1 -> v2:
- Rebased to upstream and phs_mem_alloc simplifications
-- Upsteam added the "map_offset" parameter to many RAM allocation
interfaces.
- "softmmu/physmem: Drop "shared" parameter from ram_block_add()"
-- Use local variable "shared"
- "memory: introduce RAM_NORESERVE and wire it up in qemu_ram_mmap()"
-- Simplify due to phs_mem_alloc changes
- "util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE"
-- Add a whole bunch of comments.
-- Exclude shared anonymous memory that QEMU doesn't use
-- Special-case readonly mappings
Cc: Peter Xu <pet...@redhat.com>
Cc: "Michael S. Tsirkin" <m...@redhat.com>
Cc: Eduardo Habkost <ehabk...@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
Cc: Richard Henderson <richard.hender...@linaro.org>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Igor Mammedov <imamm...@redhat.com>
Cc: "Philippe Mathieu-Daudé" <phi...@redhat.com>
Cc: Stefan Hajnoczi <stefa...@redhat.com>
Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
Cc: Greg Kurz <gr...@kaod.org>
Cc: Liam Merwick <liam.merw...@oracle.com>
Cc: Marcel Apfelbaum <mapfe...@redhat.com>
David Hildenbrand (12):
softmmu/physmem: Mark shared anonymous memory RAM_SHARED
softmmu/physmem: Fix ram_block_discard_range() to handle shared
anonymous memory
softmmu/physmem: Fix qemu_ram_remap() to handle shared anonymous
memory
util/mmap-alloc: Factor out calculation of the pagesize for the guard
page
util/mmap-alloc: Factor out reserving of a memory region to
mmap_reserve()
util/mmap-alloc: Factor out activating of memory to mmap_activate()
softmmu/memory: Pass ram_flags into qemu_ram_alloc_from_fd()
softmmu/memory: Pass ram_flags into
memory_region_init_ram_shared_nomigrate()
util/mmap-alloc: Pass flags instead of separate bools to
qemu_ram_mmap()
memory: introduce RAM_NORESERVE and wire it up in qemu_ram_mmap()
util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE
hostmem: Wire up RAM_NORESERVE via "reserve" property
backends/hostmem-file.c | 11 +-
backends/hostmem-memfd.c | 8 +-
backends/hostmem-ram.c | 7 +-
backends/hostmem.c | 33 +++
hw/m68k/next-cube.c | 4 +-
hw/misc/ivshmem.c | 5 +-
include/exec/cpu-common.h | 1 +
include/exec/memory.h | 43 ++--
include/exec/ram_addr.h | 9 +-
include/qemu/mmap-alloc.h | 20 +-
include/qemu/osdep.h | 3 +-
include/sysemu/hostmem.h | 2 +-
migration/ram.c | 3 +-
.../memory-region-housekeeping.cocci | 8 +-
softmmu/memory.c | 27 ++-
softmmu/physmem.c | 61 +++--
util/mmap-alloc.c | 217 ++++++++++++------
util/oslib-posix.c | 7 +-
util/oslib-win32.c | 13 +-
19 files changed, 323 insertions(+), 159 deletions(-)
--
2.29.2
