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 <rientjes@google.com>
Reported-by: Hugh Dickens <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/internal.h

@@ -180,7 +180,8 @@ static inline int mlocked_vma_newpage(struct vm_area_struct *vma,
 		return 0;
 
 	if (!TestSetPageMlocked(page)) {
-		inc_zone_page_state(page, NR_MLOCK);
+		mod_zone_page_state(page_zone(page), NR_MLOCK,
+				    hpage_nr_pages(page));
 		count_vm_event(UNEVICTABLE_PGMLOCKED);
 	}
 	return 1;

mm/mlock.c

@@ -56,7 +56,8 @@ void clear_page_mlock(struct page *page)
 	if (!TestClearPageMlocked(page))
 		return;
 
-	dec_zone_page_state(page, NR_MLOCK);
+	mod_zone_page_state(page_zone(page), NR_MLOCK,
+			    -hpage_nr_pages(page));
 	count_vm_event(UNEVICTABLE_PGCLEARED);
 	if (!isolate_lru_page(page)) {
 		putback_lru_page(page);
@@ -78,7 +79,8 @@ void mlock_vma_page(struct page *page)
 	BUG_ON(!PageLocked(page));
 
 	if (!TestSetPageMlocked(page)) {
-		inc_zone_page_state(page, NR_MLOCK);
+		mod_zone_page_state(page_zone(page), NR_MLOCK,
+				    hpage_nr_pages(page));
 		count_vm_event(UNEVICTABLE_PGMLOCKED);
 		if (!isolate_lru_page(page))
 			putback_lru_page(page);
@@ -105,7 +107,8 @@ void munlock_vma_page(struct page *page)
 	BUG_ON(!PageLocked(page));
 
 	if (TestClearPageMlocked(page)) {
-		dec_zone_page_state(page, NR_MLOCK);
+		mod_zone_page_state(page_zone(page), NR_MLOCK,
+				    -hpage_nr_pages(page));
 		if (!isolate_lru_page(page)) {
 			int ret = SWAP_AGAIN;