[Qemu-devel] Memory hotplug and ancient kernels

[Andrey Korolyov]

Hi,

with kernel with an obsolete version (< 3.8) DIMM configuration is not
working as defined in a boot-up values, though it is possible to add
dimm during runtime and it will be recognized just well. ACPI tables
and the of DMI for kernels which are recognizing on-boot modules and
for ones which are not are the same and I am barely remembering that
some changes related to memory hotplug mechanism was landed in 3.8.

Given following configuration, dimm2 is plugged during current boot
cycle of Centos 2.6.32 kernel:

'{ "execute": "query-memory-devices"}'
{"return":[{"type":"dimm","data":{"memdev":"/objects/mem0","hotplugged":false,"addr":4294967296,"hotpluggable":true,"size":134217728,"slot":0,"node":0,"id":"dimm0"}},{"type":"dimm","data":{"memdev":"/objects/mem1","hotplugged":true,"addr":4429185024,"hotpluggable":true,"size":134217728,"slot":1,"node":0,"id":"dimm1"}},{"type":"dimm","data":{"memdev":"/objects/mem2","hotplugged":true,"addr":4563402752,"hotpluggable":true,"size":134217728,"slot":2,"node":0,"id":"dimm2"}}],"id":"libvirt-16"}

Hotplug Mem Device
init_memory_mapping: 0000000110000000-0000000118000000
 0110000000 - 0118000000 page 2M
 [ffffea0003b80000-ffffea0003d7ffff] PMD ->
[ffff88001d600000-ffff88001d7fffff] on node 0
Built 1 zonelists in Node order, mobility grouping on.  Total pages: 160734
Policy zone: Normal

ls /sys/devices/system/memory/| grep mem
memory0
memory1
memory2
memory3
memory34

..Rebooting to 3.10..

ls /sys/devices/system/memory/| grep mem
memory0
memory1
memory2
memory3
memory32
memory33
memory34

The results are based on tag-2.1.2 without any modifications.