Re: [PATCH v8 00/15] RAM_NORESERVE, MAP_NORESERVE and hostmem "reserve" property

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/05/21 13:43, David Hildenbrand wrote:
> Based-on: 20210406080126.24010-1-david@redhat.com

Queued both the dependent series and this one, thanks.  Sorry for the delay.

Paolo

> 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.
> 
> Later, upper layers are expected to specify "reserve=off" only for
> memory backends assigned to virtio-mem devices, not all VM memory. To make
> mistakes by users less severe, we're, for example, working on preallocation
> of memory in virtio-mem itself, to be upstreamed later.
> 
> 
> v7 -> v8:
> - "hostmem: Wire up RAM_NORESERVE via "reserve" property"
> -- Make the "reserve" property depend on CONFIG_LINUX
> -- Add missing (since 6.1) to qom json
> - "qmp: Include "reserve" property of memory backends"
> -- Make the "reserve" value optional, depending on availability of the
>     "reserve" property
> - "hmp: Print "reserve" property of memory backends with "info memdev""
> -- Print only with "has_reserve"
> 
> v6 -> v7:
> - Collected ACKs and RBs
> - "hostmem: Wire up RAM_NORESERVE via "reserve" property"
> -- Extended qapi/qom.json documentation
> - "qmp: Include "reserve" property of memory backends"
> -- Extended property description
> 
> v5 -> v6:
> - "softmmu/memory: Pass ram_flags to memory_region_init ..."
> -- Split up into two patches
> ---> "softmmu/memory: Pass ram_flags to memory_region.."
> ---> "softmmu/memory: Pass ram_flags to qemu_ram_alloc() ..."
> -- Also set RAM_PREALLOC from qemu_ram_alloc_from_ptr()
> - Collected acks/rbs
> 
> v4 -> v5:
> - Sent out shared anonymous RAM fixes separately
> - Rebased
> - "hostmem: Wire up RAM_NORESERVE via "reserve" property"
> -- Adjusted/simplified description of new "reserve" property
> -- Properly add it to qapi/qom.json
> - "qmp: Clarify memory backend properties returned via query-memdev"
> -- Added
> - "qmp: Include "share" property of memory backends"
> -- Added
> - "hmp: Print "share" property of memory backends with "info memdev""
> - Added
> - "qmp: Include "reserve" property of memory backends"
> -- Adjust description of new "reserve" property
> 
> v3 -> v4:
> - Minor comment/description updates
> - "softmmu/physmem: Fix ram_block_discard_range() to handle shared ..."
> -- Extended description
> - "util/mmap-alloc: Pass flags instead of separate bools to ..."
> -- Move flags to include/qemu/osdep.h and rename to "QEMU_MAP_*"
> - "memory: Introduce RAM_NORESERVE and wire it up in qemu_ram_mmap()"
> -- Adjust to new flags. Handle errors in mmap_activate() for now.
> - "util/mmap-alloc: Support RAM_NORESERVE via MAP_NORESERVE under Linux"
> -- Restrict support to Linux only for now
> - "qmp: Include "reserve" property of memory backends"
> -- Added
> - "hmp: Print "reserve" property of memory backends with ..."
> -- Added
> 
> 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 <peterx@redhat.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> Cc: Greg Kurz <groug@kaod.org>
> Cc: Liam Merwick <liam.merwick@oracle.com>
> Cc: Marcel Apfelbaum <mapfelba@redhat.com>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Michal Privoznik <mprivozn@redhat.com>
> Cc: Marek Kedzierski <mkedzier@redhat.com>
> 
> David Hildenbrand (15):
>    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 to qemu_ram_alloc_from_fd()
>    softmmu/memory: Pass ram_flags to
>      memory_region_init_ram_shared_nomigrate()
>    softmmu/memory: Pass ram_flags to qemu_ram_alloc() and
>      qemu_ram_alloc_internal()
>    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 under Linux
>    hostmem: Wire up RAM_NORESERVE via "reserve" property
>    qmp: Clarify memory backend properties returned via query-memdev
>    qmp: Include "share" property of memory backends
>    hmp: Print "share" property of memory backends with "info memdev"
>    qmp: Include "reserve" property of memory backends
>    hmp: Print "reserve" property of memory backends with "info memdev"
> 
>   backends/hostmem-file.c                       |  11 +-
>   backends/hostmem-memfd.c                      |   8 +-
>   backends/hostmem-ram.c                        |   7 +-
>   backends/hostmem.c                            |  36 +++
>   hw/core/machine-hmp-cmds.c                    |   6 +
>   hw/core/machine-qmp-cmds.c                    |   8 +
>   hw/m68k/next-cube.c                           |   4 +-
>   hw/misc/ivshmem.c                             |   5 +-
>   include/exec/cpu-common.h                     |   1 +
>   include/exec/memory.h                         |  42 ++--
>   include/exec/ram_addr.h                       |   9 +-
>   include/qemu/mmap-alloc.h                     |  16 +-
>   include/qemu/osdep.h                          |  30 ++-
>   include/sysemu/hostmem.h                      |   2 +-
>   migration/ram.c                               |   3 +-
>   qapi/machine.json                             |  16 +-
>   qapi/qom.json                                 |  10 +
>   .../memory-region-housekeeping.cocci          |   8 +-
>   softmmu/memory.c                              |  27 ++-
>   softmmu/physmem.c                             |  51 +++--
>   util/mmap-alloc.c                             | 212 +++++++++++++-----
>   util/oslib-posix.c                            |   7 +-
>   util/oslib-win32.c                            |  13 +-
>   23 files changed, 374 insertions(+), 158 deletions(-)
>