diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index 02e1204971b0a823e7ce8350872390d825219c48..c0138cb19705bcf9e5a0e7b6f5681a170185ede2 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -33,9 +33,16 @@ endif
 # LDLIBS.
 MAKEFLAGS += --no-builtin-rules
 
-CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES) $(TOOLS_INCLUDES)
+CFLAGS = -Wall -O2 -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES) $(TOOLS_INCLUDES)
 LDLIBS = -lrt -lpthread -lm
 
+# Some distributions (such as Ubuntu) configure GCC so that _FORTIFY_SOURCE is
+# automatically enabled at -O1 or above. This triggers various unused-result
+# warnings where functions such as read() or write() are called and their
+# return value is not checked. Disable _FORTIFY_SOURCE to silence those
+# warnings.
+CFLAGS += -U_FORTIFY_SOURCE
+
 TEST_GEN_FILES = cow
 TEST_GEN_FILES += compaction_test
 TEST_GEN_FILES += gup_longterm