tools/mm/page_owner_sort: add help option support

Add -h/--help option to display usage information and improve code style.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ye Liu <[e-mail]>
Cc: SeongJae Park <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/mm/page_owner_sort.c

···
 		{ "pid", required_argument, NULL, 1 },
 		{ "tgid", required_argument, NULL, 2 },
 		{ "name", required_argument, NULL, 3 },
-		{ "cull",  required_argument, NULL, 4 },
-		{ "sort",  required_argument, NULL, 5 },
+		{ "cull", required_argument, NULL, 4 },
+		{ "sort", required_argument, NULL, 5 },
+		{ "help", no_argument, NULL, 'h' },
 		{ 0, 0, 0, 0},
 	};
 
 	compare_flag = COMP_NO_FLAG;
 
-	while ((opt = getopt_long(argc, argv, "admnpstP", longopts, NULL)) != -1)
+	while ((opt = getopt_long(argc, argv, "admnpstPh", longopts, NULL)) != -1)
 		switch (opt) {
 		case 'a':
 			compare_flag |= COMP_ALLOC;
···
 		case 'n':
 			compare_flag |= COMP_COMM;
 			break;
+		case 'h':
+			usage();
+			exit(0);
 		case 1:
 			filter = filter | FILTER_PID;
 			fc.pids = parse_nums_list(optarg, &fc.pids_size);