Re: [PATCH v2 2/2] dax: add a sysfs knob to control memmap_on_memory behavior

[Zhijian Li (Fujitsu)]

On 08/12/2023 03:25, Verma, Vishal L wrote:
> On Thu, 2023-12-07 at 08:29 +0000, Zhijian Li (Fujitsu) wrote:
>> Hi Vishal,
>>
>>
>> On 07/12/2023 12:36, Vishal Verma wrote:
>>> +
>>> +What:          /sys/bus/dax/devices/daxX.Y/memmap_on_memory
>>> +Date:          October, 2023
>>> +KernelVersion: v6.8
>>> +Contact:       nvdimm@xxxxxxxxxxxxxxx
>>> +Description:
>>> +               (RW) Control the memmap_on_memory setting if the dax device
>>> +               were to be hotplugged as system memory. This determines whether
>>> +               the 'altmap' for the hotplugged memory will be placed on the
>>> +               device being hotplugged (memmap_on+memory=1) or if it will be
>>
>> s/memmap_on+memory=1/memmap_on_memory=1
> 
> Thanks, will fix.
>>
>>
>> I have a question here
>>
>> What relationship about memmap_on_memory and 'ndctl-create-namespace
>> -M' option which
>> specifies where is the vmemmap backed memory.
>> I'm confused that memmap_on_memory=1 and '-M dev' are the same for
>> nvdimm devdax mode ?
>>
> The main difference is that memory that comes from non-nvdimm sources,
> such as hmem, or cxl, doesn't have a chance to set up the altmaps as
> pmem can with '-M dev'. For these, memmap_on_memory does this as part
> of the memory hotplug.

Thanks for your explanation.
(I wrongly thought nvdimm.kmem was also controlled by '-M dev' before)

feel free add:
Tested-by: Li Zhijian <lizhijian@xxxxxxxxxxx>