Re: [RFC 9/9] prd: Add support for page struct mapping

[Boaz Harrosh <openosd@gmail.com>]

On 08/15/2014 11:28 PM, Toshi Kani wrote:
> On Wed, 2014-08-13 at 15:26 +0300, Boaz Harrosh wrote:
>> From: Yigal Korman <yigal@plexistor.com>
>>
<>
>>
>> All is actually needed for this is to allocate page-sections
>> and map them into kernel virtual memory. Note that these sections
>> are not associated with any zone, because that would add them to
>> the page_allocators.
> 
> Can we just use memory hotplug and call add_memory(), instead of
> directly calling sparse_add_one_section()?  Memory hotplug adds memory
> as off-line state, and sets all pages reserved.  So, I do not think the
> page allocators will mess with them (unless you put them online).  It
> can also maps the pages with large page size.
> 
> Thanks,
> -Toshi
> 

Thank you Toshi for your reply

I was thinking about that as well at first, but I was afraid, once I call
add_memory() what will prevent the user from enabling that memory through the sysfs
interface later, it looks to me that add_memory() will add all the necessary knobs
to do it.

It is very important to keep a clear distinction, pmem is *not* memory what-so-ever
it is however memory-mapped and needs these accesses enabled for it, hence the need
for page-struct so we can DMA it off the buss.

I am very afraid of any thing that will associate a "zone" with this memory.
Also the:
	firmware_map_add_hotplug(start, start + size, "System RAM");

"System RAM" it is not. And also I think that for DDR4 NvDIMMs we will fail with:
	ret = check_hotplug_memory_range(start, size);

Thanks
Boaz

> 
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