Re: [RFC 2/2] x86_64, mm: Reinsert the absent memory

["H. Peter Anvin" <hpa@zytor.com>]

On 06/23/2013 02:32 AM, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@kernel.org> wrote:
> 
>> Yet another thing to consider would be to implement an initialization 
>> speedup of 3 orders of magnitude: initialize on the large page (2MB) 
>> grandularity and on-demand delay the initialization of the 4K granular 
>> struct pages [but still allocating them] - which I suspect are a good 
>> chunk of the overhead? That way we could initialize in 2MB steps and speed 
>> up the 2 hours bootup of 32 TB of RAM to 14 seconds...
>>
>> [ The cost would be one more branch in the buddy allocator, to detect
>>   not-yet-initialized 2 MB chunks as we encounter them. Acceptable I 
>>   think. ]
> 
> One advantage of this scheme would be that we could use it on pretty much 
> any box, it would provide instant boot time speedups everywhere [a couple 
> of hundred msecs on a small 4GB box - significant I think] - and would 
> spread out and parallelize initialization to later stages.
> 

Even better if we could start at the 1 GB level, which most of these
really huge machines will have hardware support for.

	-hpa