kmemleak: Show the age of an unreferenced object

The jiffies shown for unreferenced objects isn't always meaningful to
people debugging kernel memory leaks. This patch adds the age as well to
the displayed information.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

mm/kmemleak.c

@@ -346,11 +346,13 @@ static void print_unreferenced(struct seq_file *seq,
 			       struct kmemleak_object *object)
 {
 	int i;
+	unsigned int msecs_age = jiffies_to_msecs(jiffies - object->jiffies);
 
 	seq_printf(seq, "unreferenced object 0x%08lx (size %zu):\n",
 		   object->pointer, object->size);
-	seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu\n",
-		   object->comm, object->pid, object->jiffies);
+	seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu (age %d.%03ds)\n",
+		   object->comm, object->pid, object->jiffies,
+		   msecs_age / 1000, msecs_age % 1000);
 	hex_dump_object(seq, object);
 	seq_printf(seq, "  backtrace:\n");