selftests/vm: use memfd for hugetlb-madvise test

For dropping the hugetlb mountpoint in run_vmtests.sh. Since no parameter
is needed, drop USAGE too.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Peter Xu <[e-mail]>
Cc: Axel Rasmussen <[e-mail]>
Cc: Mike Kravetz <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/testing/selftests/vm/hugetlb-madvise.c

···
  * directory.
  */
 
+#define _GNU_SOURCE
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
···
 #define __USE_GNU
 #include <fcntl.h>
 
-#define USAGE	"USAGE: %s <hugepagefile_name>\n"
 #define MIN_FREE_PAGES	20
 #define NR_HUGE_PAGES	10	/* common number of pages to map/allocate */
 
···
 	int fd;
 	int ret;
 
-	if (argc != 2) {
-		printf(USAGE, argv[0]);
-		exit(1);
-	}
-
 	huge_page_size = default_huge_page_size();
 	if (!huge_page_size) {
 		printf("Unable to determine huge page size, exiting!\n");
···
 		exit(1);
 	}
 
-	fd = open(argv[1], O_CREAT | O_RDWR, 0755);
+	fd = memfd_create(argv[0], MFD_HUGETLB);
 	if (fd < 0) {
-		perror("Open failed");
+		perror("memfd_create() failed");
 		exit(1);
 	}
 
···
 	(void)munmap(addr2, NR_HUGE_PAGES * huge_page_size);
 
 	close(fd);
-	unlink(argv[1]);
 	return 0;
 }