diff --git a/tools/mm/page_owner_sort.c b/tools/mm/page_owner_sort.c
index a5b61b4abc2f..6c2ac5d9dc4b 100644
--- a/tools/mm/page_owner_sort.c
+++ b/tools/mm/page_owner_sort.c
@@ -772,6 +772,15 @@ static void usage(void)
 		"\t\t\targument in the form of a comma-separated list with some\n"
 		"\t\t\tcommon fields predefined (pid, tgid, comm, stacktrace, allocator, module)\n"
 		"--sort <order>\t\tSpecify sort order as: [+|-]key[,[+|-]key[,...]]\n"
+		"\t\t\tAvailable keys:\n"
+		"\t\t\t  pid(p), tgid(tg), name(n), stacktrace(st),\n"
+		"\t\t\t  txt(T), alloc_ts(at), allocator(ator), module(mod)\n"
+		"\t\t\tThe \"+\" is optional since default direction is\n"
+		"\t\t\tincreasing numerical or lexicographic order.\n"
+		"\t\t\tMixed use of abbreviated and complete-form is allowed.\n"
+		"\t\t\tExamples:\n"
+		"\t\t\t  --sort=n,+pid,-tgid\n"
+		"\t\t\t  --sort=mod,at\n"
 	);
 }