hugetlb: parallelize 2M hugetlb allocation and initialization

By distributing both the allocation and the initialization tasks across
multiple threads, the initialization of 2M hugetlb will be faster, thereby
improving the boot speed.

Here are some test results:
      test case        no patch(ms)   patched(ms)   saved
 ------------------- -------------- ------------- --------
  256c2T(4 node) 2M           3336          1051   68.52%
  128c1T(2 node) 2M           1943           716   63.15%

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Gang Li <[email protected]>
Tested-by: David Rientjes <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Daniel Jordan <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jane Chu <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Steffen Klassert <[email protected]>
Cc: Tim Chen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions