On 1/23/2026 10:43 AM, fanhuang wrote:
Hi all,
This is v5 of the SPM (Specific Purpose Memory) patch. Thank you for
the feedback on v4.
Changes in v5:
- Renamed 'spm=on|off' to 'memmap-type=normal|spm|reserved' enum
(per Gregory's suggestion for better extensibility)
- Updated QAPI schema with new NumaMemmapType enum
- Updated documentation to describe SPM as a policy hint
(per Jonathan's feedback)
Use case:
This feature allows marking NUMA node memory as Specific Purpose Memory
(SPM) or reserved in the E820 table. SPM serves as a hint to the guest
that this memory might be managed by device drivers based on guest policy
Example usage:
-object memory-backend-ram,size=8G,id=m0
-object memory-backend-memfd,size=8G,id=m1
-numa node,nodeid=0,memdev=m0
-numa node,nodeid=1,memdev=m1,memmap-type=spm
Supported memmap-type values:
- normal: Regular system RAM (E820 type 1, default)
- spm: Specific Purpose Memory (E820 type 0xEFFFFFFF), a hint
that this memory might be managed by device drivers
- reserved: Reserved memory (E820 type 2), not usable as RAM
Please review. Thanks!
Best regards,
Jerry Huang
Hi all,
Here are the OS-facing test results showing E820 and ACPI SRAT data for
different memmap-type configurations:
1. memmap-type=spm
~~~~~~~~~~~~~~~~~~
-numa node,cpus=4-7,nodeid=1,memdev=m1,memmap-type=spm
Guest dmesg output:
[ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000027fffffff]
usable
[ 0.000000] BIOS-e820: [mem 0x0000000280000000-0x000000047fffffff]
soft reserved
[ 0.000000] BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff]
reserved
[ 0.042578] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x0009ffff]
[ 0.042580] ACPI: SRAT: Node 0 PXM 0 [mem 0x00100000-0x7fffffff]
[ 0.042581] ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0x27fffffff]
[ 0.042582] ACPI: SRAT: Node 1 PXM 1 [mem 0x280000000-0x47fffffff]
2. memmap-type=reserved
~~~~~~~~~~~~~~~~~~~~~~~
-numa node,cpus=4-7,nodeid=1,memdev=m1,memmap-type=reserved
Guest dmesg output:
[ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000027fffffff]
usable
[ 0.000000] BIOS-e820: [mem 0x0000000280000000-0x000000047fffffff]
reserved
[ 0.000000] BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff]
reserved
[ 0.042728] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x0009ffff]
[ 0.042729] ACPI: SRAT: Node 0 PXM 0 [mem 0x00100000-0x7fffffff]
[ 0.042731] ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0x27fffffff]
[ 0.042732] ACPI: SRAT: Node 1 PXM 1 [mem 0x280000000-0x47fffffff]
3. normal (default, no memmap-type specified)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-numa node,cpus=4-7,nodeid=1,memdev=m1
Guest dmesg output:
[ 0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000047fffffff]
usable
[ 0.000000] BIOS-e820: [mem 0x000000fd00000000-0x000000ffffffffff]
reserved
[ 0.042413] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x0009ffff]
[ 0.042414] ACPI: SRAT: Node 0 PXM 0 [mem 0x00100000-0x7fffffff]
[ 0.042416] ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0x27fffffff]
[ 0.042417] ACPI: SRAT: Node 1 PXM 1 [mem 0x280000000-0x47fffffff]
The results show:
- Node association is correct (Node 1 at 0x280000000-0x47fffffff)
- E820 types are correctly applied (usable/soft reserved/reserved)
- SRAT entries are generated for all configurations
