pagemap: return map count, not reference count, in /proc/kpagecount

Since pagemap is all about examining pages mapped into processes' memory
spaces, it makes sense for kpagecount to return the map counts, not the
reference counts.
Signed-off-by: NThomas Tuttle <ttuttle@google.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/proc/proc_misc.c

@@ -726,7 +726,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
 		if (!ppage)
 			pcount = 0;
 		else
-			pcount = atomic_read(&ppage->_count);
+			pcount = page_mapcount(ppage);
 
 		if (put_user(pcount, out++)) {
 			ret = -EFAULT;