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[Qemu-devel] [Question] inconsistent memory amount statistics

From: David Hildenbrand
Subject: [Qemu-devel] [Question] inconsistent memory amount statistics
Date: Fri, 22 Jun 2018 09:41:15 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

Starting qemu with and querying some outputs:

-m 4G,maxmem=20G,slots=2 \
-numa node,nodeid=0,cpus=0-1 -numa node,nodeid=1,cpus=2-3 \
-device virtio-balloon \
-object memory-backend-ram,id=mem0,size=8G \
-device pc-dimm,id=dimm0,memdev=mem0 \
-object memory-backend-ram,id=mem1,size=8G \
-device nvdimm,id=dimm1,memdev=mem1,node=1

(qemu) info numa
info numa
2 nodes
node 0 cpus: 0 1
node 0 size: 10240 MB
node 0 plugged: 0 MB
node 1 cpus: 2 3
node 1 size: 10240 MB
node 1 plugged: 0 MB

(qemu) info memory_size_summary
info memory_size_summary
base memory: 4294967296
plugged memory: 17179869184

(qemu) info memory-devices
info memory-devices
Memory device [dimm]: "dimm0"
  addr: 0x140000000
  slot: 0
  node: 0
  size: 8589934592
  memdev: /objects/mem0
  hotplugged: false
  hotpluggable: true
Memory device [nvdimm]: "dimm1"
  addr: 0x340000000
  slot: 1
  node: 1
  size: 8589934592
  memdev: /objects/mem1
  hotplugged: false
  hotpluggable: true

(qemu) info balloon
info balloon
balloon: actual=12288

1. "info numa"
- considers both, pc-dimm and nvdimm
- "-device ..." are considered as "!plugged" although it could be
  theoretically "unplugged"
- device_add devices are considered as "plugged"

2. "info memory_size_summary"
- considers both, pc-dimm and nvdimm
- "-device ..." are considered as "plugged"
- device_add devices are considered as "plugged"

3. "info balloon"
- does not consider nvdimm devices to calculate "actual"
-- actual = get_current_ram_size() - inflated
-- get_current_ram_size() does not consider nvdimm

So we have some inconsistency in regards of
1. What is considered memory and what not (pc-dimm vs nvdimm)
2. What is considered plugged memory (-device vs. device_add)

Is this what we expect? I think we should make up our mind

a) what "plugged" means
b) which stats should consider "nvdimm" and which not.

I would have guessed that "nvdimms" might be memory devices but should
never count towards memory statistics ("not actually ram" - they might
be OK).

Especially "info memory_size_summary" ... "plugged-memory - amount of
memory that was hot-plugged" - this seems to be wrong. And I wonder if
we should exclude nvdimm from that.



David / dhildenb

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