From: Christoph Hellwig <hch@lst.de>

This patch is from the IA64 tree, with some minor cleanups by me.
David described it as:

  This is a performance speed up and some minor indendation fixups.

  The problem is that the bootmem code is (a) hugely slow and (b) has
  execution that grow quadratically with the size of the bootmap bitmap.
  This causes noticable slowdowns, especially on machines with (relatively)
  large holes in the physical memory map.  Issue (b) is addressed by
  maintaining the "last_success" cache, so that we start the next search
  from the place where we last found some memory (this part of the patch
  could stand additional reviewing/testing).  Issue (a) is addressed by
  using find_next_zero_bit() instead of the slow bit-by-bit testing.