selftests: mm: perform some system cleanup before using hugepages

When running with CATEGORY= (thp | hugetlb) we see a large numbers of
tests failing.  These failures are due to not being able to allocate a
hugepage and normally occur on memory contrainted systems or when using
large page sizes.

drop_cache and compact_memory before the tests for a higher chance at a
successful hugepage allocation.

Link: https://lkml.kernel.org/r/20240117180037.15734-1-npache@redhat.com
Signed-off-by: Nico Pache <npache@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/run_vmtests.sh

@@ -206,6 +206,15 @@ pretty_name() {
 # Usage: run_test [test binary] [arbitrary test arguments...]
 run_test() {
 	if test_selected ${CATEGORY}; then
+		# On memory constrainted systems some tests can fail to allocate hugepages.
+		# perform some cleanup before the test for a higher success rate.
+		if [ ${CATEGORY} == "thp" ] | [ ${CATEGORY} == "hugetlb" ]; then
+			echo 3 > /proc/sys/vm/drop_caches
+			sleep 2
+			echo 1 > /proc/sys/vm/compact_memory
+			sleep 2
+		fi
+
 		local test=$(pretty_name "$*")
 		local title="running $*"
 		local sep=$(echo -n "$title" | tr "[:graph:][:space:]" -)