On Mon 13-03-17 11:31:10, Igor Mammedov wrote:

On Fri, 10 Mar 2017 14:58:07 +0100

[...]

quoted

[    0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x00000000-0x0009ffff]
[    0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x00100000-0x3fffffff]
[    0.000000] ACPI: SRAT: Node 1 PXM 1 [mem 0x40000000-0x7fffffff]
[    0.000000] ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0x27fffffff] hotplug
[    0.000000] NUMA: Node 0 [mem 0x00000000-0x0009ffff] + [mem 0x00100000-0x3fffffff] -> [mem 0x00000000-0x3fffffff]
[    0.000000] NODE_DATA(0) allocated [mem 0x3fffc000-0x3fffffff]
[    0.000000] NODE_DATA(1) allocated [mem 0x7ffdc000-0x7ffdffff]
[    0.000000] Zone ranges:
[    0.000000]   DMA      [mem 0x0000000000001000-0x0000000000ffffff]
[    0.000000]   DMA32    [mem 0x0000000001000000-0x000000007ffdffff]
[    0.000000]   Normal   empty
[    0.000000] Movable zone start for each node
[    0.000000] Early memory node ranges
[    0.000000]   node   0: [mem 0x0000000000001000-0x000000000009efff]
[    0.000000]   node   0: [mem 0x0000000000100000-0x000000003fffffff]
[    0.000000]   node   1: [mem 0x0000000040000000-0x000000007ffdffff]

so there is neither any normal zone nor movable one at the boot time.

it could be if hotpluggable memory were present at boot time in E802 table
(if I remember right when running on hyperv there is movable zone at boot time),

but in qemu hotpluggable memory isn't put into E820,
so zone is allocated later when memory is enumerated
by ACPI subsystem and onlined.
It causes less issues wrt movable zone and works for
different versions of linux/windows as well.

That's where in kernel auto-onlining could be also useful,
since user would be able to start-up with with small
non removable memory plus several removable DIMMs
and have all the memory onlined/available by the time
initrd is loaded. (missing piece here is onling
removable memory as movable by default).

Why we should even care to online that memory that early rather than
making it available via e820?
 

quoted

Then I hotplugged 1G slot
(qemu) object_add memory-backend-ram,id=mem1,size=1G
(qemu) device_add pc-dimm,id=dimm1,memdev=mem1

You can also specify node a pc-dimm goes to with 'node' property
if it should go to other then node 0.

device_add pc-dimm,id=dimm1,memdev=mem1,node=1

thanks for the tip

quoted

unfortunatelly the memory didn't show up automatically and I got
[  116.375781] acpi PNP0C80:00: Enumeration failure

it should work,
do you have CONFIG_ACPI_HOTPLUG_MEMORY enabled?

No I didn't. Thanks, good to know!
-- 
Michal Hocko
SUSE Labs

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