selftests/vm/compaction_test: fix write to restore nr_hugepages

The write at the end of the test to restore nr_hugepages to its previous
value is failing.  This is because it is trying to write the number of
bytes in the char array as opposed to the number of bytes in the string.

Link: http://lkml.kernel.org/r/1465331205-3284-1-git-send-email-mike.kravetz@oracle.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Sri Jayaramappa <sjayaram@akamai.com>
Cc: Eric B Munson <emunson@akamai.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

tools/testing/selftests/vm/compaction_test.c

@@ -136,7 +136,7 @@ int check_compaction(unsigned long mem_free, unsigned int hugepage_size)
 	printf("No of huge pages allocated = %d\n",
 	       (atoi(nr_hugepages)));
 
-	if (write(fd, initial_nr_hugepages, sizeof(initial_nr_hugepages))
+	if (write(fd, initial_nr_hugepages, strlen(initial_nr_hugepages))
 	    != strlen(initial_nr_hugepages)) {
 		perror("Failed to write to /proc/sys/vm/nr_hugepages\n");
 		goto close_fd;