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Re: [Qemu-devel] [PATCH v3 22/32] nvdimm: init the address region used b


From: Xiao Guangrong
Subject: Re: [Qemu-devel] [PATCH v3 22/32] nvdimm: init the address region used by NVDIMM ACPI
Date: Tue, 20 Oct 2015 01:56:04 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0



On 10/19/2015 06:42 PM, Igor Mammedov wrote:
On Mon, 19 Oct 2015 18:01:17 +0800
Xiao Guangrong <address@hidden> wrote:



On 10/19/2015 05:46 PM, Igor Mammedov wrote:
On Mon, 19 Oct 2015 12:17:22 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

On Mon, Oct 19, 2015 at 03:44:13PM +0800, Xiao Guangrong wrote:


On 10/19/2015 03:39 PM, Michael S. Tsirkin wrote:
On Mon, Oct 19, 2015 at 03:27:21PM +0800, Xiao Guangrong wrote:
+        nvdimm_init_memory_state(&pcms->nvdimm_memory,
system_memory, machine,
+                                 TARGET_PAGE_SIZE);
+

Shouldn't this be conditional on presence of the nvdimm device?


We will enable hotplug on nvdimm devices in the near future once
Linux driver is ready. I'd keep it here for future development.

No, I don't think we should add stuff unconditionally. If not
nvdimm, some other flag should indicate user intends to hotplug
things.


Actually, it is not unconditionally which is called if parameter
"-m aaa, maxmem=bbb" (aaa < bbb) is used. It is on the some path
of memoy-hotplug initiation.


Right, but that's not the same as nvdimm.


it could be pc-machine property, then it could be turned on like
this: -machine nvdimm_support=on

Er, I do not understand why this separate switch is needed and why
nvdimm and pc-dimm is different. :(

NVDIMM reuses memory-hotplug's framework, such as maxmem, slot, and
dimm device, even some of ACPI logic to do hotplug things, etc. Both
nvdimm and pc-dimm are built on the same infrastructure.
NVDIMM support consumes precious low RAM  and MMIO resources and
not small amount at that. So turning it on unconditionally with
memory hotplug even if NVDIMM wouldn't ever be used isn't nice.

Okay, understand... will introduce nvdimm_support as your suggestion.
Thank you, Igor and Michael!




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