mm: fix some trivial typos in comments

Fix some trivial typos in comments.
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: <sworddragon2@aol.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Jianguo Wu <wujianguo@huawei.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -309,7 +309,7 @@ static int __meminit move_pfn_range_left(struct zone *z1, struct zone *z2,
 	/* can't move pfns which are higher than @z2 */
 	if (end_pfn > zone_end_pfn(z2))
 		goto out_fail;
-	/* the move out part mast at the left most of @z2 */
+	/* the move out part must be at the left most of @z2 */
 	if (start_pfn > z2->zone_start_pfn)
 		goto out_fail;
 	/* must included/overlap */

mm/page_alloc.c

@@ -2845,7 +2845,7 @@ EXPORT_SYMBOL(free_pages_exact);
  * nr_free_zone_pages() counts the number of counts pages which are beyond the
  * high watermark within all zones at or below a given zone index.  For each
  * zone, the number of pages is calculated as:
- *     present_pages - high_pages
+ *     managed_pages - high_pages
  */
 static unsigned long nr_free_zone_pages(int offset)
 {