mm: memmap_init: iterate over memblock regions rather that check each PFN

When called during boot the memmap_init_zone() function checks if each PFN
is valid and actually belongs to the node being initialized using
early_pfn_valid() and early_pfn_in_nid().

Each such check may cost up to O(log(n)) where n is the number of memory
banks, so for large amount of memory overall time spent in early_pfn*()
becomes substantial.

Since the information is anyway present in memblock, we can iterate over
memblock memory regions in memmap_init() and only call memmap_init_zone()
for PFN ranges that are know to be valid and in the appropriate node.

[[email protected]: fix a compilation warning from Clang]
  Link: http://lkml.kernel.org/r/[email protected]
[[email protected]: fix the incorrect hole in fast_isolate_freepages()]
  Link: http://lkml.kernel.org/r/[email protected]
  Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Baoquan He <[email protected]>
Signed-off-by: Mike Rapoport <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Tested-by: Hoan Tran <[email protected]>	[arm64]
Cc: Brian Cain <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Greentime Hu <[email protected]>
Cc: Greg Ungerer <[email protected]>
Cc: Guan Xuetao <[email protected]>
Cc: Guo Ren <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Ley Foon Tan <[email protected]>
Cc: Mark Salter <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Max Filippov <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Nick Hu <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Russell King <[email protected]>
Cc: Stafford Horne <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Vineet Gupta <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Cc: Qian Cai <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

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