mm, thp: fix mlock statistics

mm, thp: fix mlock statistics

NR_MLOCK is only accounted in single page units: there's no logic to
handle transparent hugepages.  This patch checks the appropriate number of
pages to adjust the statistics by so that the correct amount of memory is
reflected.

Currently:

		$ grep Mlocked /proc/meminfo
		Mlocked:           19636 kB

	#define MAP_SIZE	(4 << 30)	/* 4GB */

	void *ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE,
			 MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
	mlock(ptr, MAP_SIZE);

		$ grep Mlocked /proc/meminfo
		Mlocked:           29844 kB

	munlock(ptr, MAP_SIZE);

		$ grep Mlocked /proc/meminfo
		Mlocked:           19636 kB

And with this patch:

		$ grep Mlock /proc/meminfo
		Mlocked:           19636 kB

	mlock(ptr, MAP_SIZE);

		$ grep Mlock /proc/meminfo
		Mlocked:         4213664 kB

	munlock(ptr, MAP_SIZE);

		$ grep Mlock /proc/meminfo
		Mlocked:           19636 kB

Signed-off-by: David Rientjes <[email protected]>
Reported-by: Hugh Dickens <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Reviewed-by: Andrea Arcangeli <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: KAMEZAWA Hiroyuki <[email protected]>
Cc: Johannes Weiner <[email protected]>
Reviewed-by: Michel Lespinasse <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>