[PATCH v2] makedumpfile: request the kernel do page scans

[Cliff Wickman]

An update on testing thise patches:

> This version of the patch improves the consolidation of the mem_map table
> that is passed to the kernel.  See make_kernel_mmap().
> Particularly the seemingly duplicate pfn ranges generated on an older
> (2.6.32-based, rhel6) kernel.


On a 2TB machine (idle) machine:
  the crash kernel ran successfully in 512M
  the scan for unnecessary pages takes about 40 seconds
  it was a single scan, not cyclic
  
On a 16TB machine (idle) machine:
  the crash kernel ran successfully in 512M
  there is a pause of about 4 minutes during makedumpfile initialization
  the scan for unnecessary pages takes about 4.8 minutes
  it was a single scan, not cyclic