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

[Dave Hansen <dave.hansen@intel.com>]

On 09/09/2014 09:16 AM, Boaz Harrosh wrote:
> On 08/22/2014 05:36 PM, Dave Hansen wrote:
>> Is there a reason you don't just do this at boot and have to use hotplug
>> at runtime for it?  
> 
> This is a plug and play thing. This memory region is not reached via memory
> controller, it is on the ACPI/SBUS device with physical address/size specified
> there. On load of block-device this will be called. Also a block device can
> be unloaded and should be able to cleanup.

OK, cool.

>> What are the ratio of pmem to RAM?  Is it possible
>> to exhaust all of RAM with 'struct page's for pmem?
> 
> Yes! in the not very distant future there will be systems that have only pmem.
> yes no RAM. This is because once available some pmem has much better power
> efficiency then DRAM, because of the no refresh thing. So even cellphones and
> embedded system first.
...
> So the Admin/setup will need to calculate and configure the proper ratio of
> volatile vs non-volatile portions of its system for proper usage.

I'm just worried that somebody will plug a card in, and immediately OOM
the system.  Or, even worse, a card gets plugged in and 98% of the RAM
gets used by this prd driver and the kernel performs horribly.

I think we probably need to have some tracking of how much memory is
getting used for these mem_map[]s, and make sure they don't get out of hand.

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