[PATCH v5 05/14] selftests/mm: fix cgroup task placement and drop memory.current checks in hugetlb_reparenting_test.sh

Sayali Patil
2026-04-14T08:23:00Z

The test currently moves the calling shell ($$) into the target cgroup
before executing write_to_hugetlbfs. This results in the shell and any
intermediate allocations being charged to the cgroup, introducing noise
and nondeterminism in accounting. It also requires moving the shell back
to the root cgroup after execution.

Spawn a helper process that joins the target cgroup and
exec()'s write_to_hugetlbfs. This ensures that only the workload is
accounted to the cgroup and avoids unintended charging from the shell.

The test currently validates both hugetlb usage and memory.current.
However, memory.current includes internal memcg allocations and
per-CPU batched accounting (MEMCG_CHARGE_BATCH), which are not
synchronized and can vary across systems, leading to
non-deterministic results.

Since hugetlb memory is accounted via hugetlb.<size>.current,
memory.current is not a reliable indicator here. Drop memory.current
checks and rely only on hugetlb controller statistics for stable
and accurate validation.

Fixes: 29750f71a9b4 ("hugetlb_cgroup: add hugetlb_cgroup reservation tests")
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Sayali Patil <sayalip@linux.ibm.com>
---
.../selftests/mm/hugetlb_reparenting_test.sh | 41 ++++++++-----------
1 file changed, 17 insertions(+), 24 deletions(-)

diff --git a/tools/testing/selftests/mm/hugetlb_reparenting_test.sh b/tools/testing/selftests/mm/hugetlb_reparenting_test.sh
index 00f3f3cd8909..014201cb6427 100755
--- a/tools/testing/selftests/mm/hugetlb_reparenting_test.sh
+++ b/tools/testing/selftests/mm/hugetlb_reparenting_test.sh
@@ -105,22 +105,17 @@ function assert_with_retry() {
}

function assert_state() {
- local expected_a="$1"
- local expected_a_hugetlb="$2"
- local expected_b=""
+ local expected_a_hugetlb="$1"
local expected_b_hugetlb=""

- if [ ! -z ${3:-} ] && [ ! -z ${4:-} ]; then
- expected_b="$3"
- expected_b_hugetlb="$4"
+ if [ ! -z ${2:-} ]; then
+ expected_b_hugetlb="$2"
fi

- assert_with_retry "$CGROUP_ROOT/a/memory.$usage_file" "$expected_a"
assert_with_retry \
"$CGROUP_ROOT/a/hugetlb.${MB_DISPLAY}${UNIT}.$usage_file" "$expected_a_hugetlb"

- if [[ -n "$expected_b" && -n "$expected_b_hugetlb" ]]; then
- assert_with_retry "$CGROUP_ROOT/a/b/memory.$usage_file" "$expected_b"
+ if [[ -n "$expected_b_hugetlb" ]]; then
assert_with_retry \
"$CGROUP_ROOT/a/b/hugetlb.${MB_DISPLAY}${UNIT}.$usage_file" "$expected_b_hugetlb"
fi
@@ -154,18 +149,16 @@ write_hugetlbfs() {
local size="$3"

if [[ $cgroup2 ]]; then
- echo $$ >$CGROUP_ROOT/$cgroup/cgroup.procs
+ cg_file="$CGROUP_ROOT/$cgroup/cgroup.procs"
else
echo 0 >$CGROUP_ROOT/$cgroup/cpuset.mems
echo 0 >$CGROUP_ROOT/$cgroup/cpuset.cpus
- echo $$ >"$CGROUP_ROOT/$cgroup/tasks"
- fi
- ./write_to_hugetlbfs -p "$path" -s "$size" -m 0 -o
- if [[ $cgroup2 ]]; then
- echo $$ >$CGROUP_ROOT/cgroup.procs
- else
- echo $$ >"$CGROUP_ROOT/tasks"
+ cg_file="$CGROUP_ROOT/$cgroup/tasks"
fi
+
+ # Spawn helper to join cgroup before exec to ensure correct cgroup accounting
+ bash -c "echo \$\$ > '$cg_file'; exec ./write_to_hugetlbfs -p '$path' -s '$size' -m 0 -o" & pid=$!
+ wait "$pid"
echo
}

@@ -203,21 +196,21 @@ if [[ ! $cgroup2 ]]; then
write_hugetlbfs a "$MNT"/test $size

echo Assert memory charged correctly for parent use.
- assert_state 0 $size 0 0
+ assert_state $size 0

write_hugetlbfs a/b "$MNT"/test2 $size

echo Assert memory charged correctly for child use.
- assert_state 0 $(($size * 2)) 0 $size
+ assert_state $(($size * 2)) $size

rmdir "$CGROUP_ROOT"/a/b
echo Assert memory reparent correctly.
- assert_state 0 $(($size * 2))
+ assert_state $(($size * 2))

rm -rf "$MNT"/*
umount "$MNT"
echo Assert memory uncharged correctly.
- assert_state 0 0
+ assert_state 0

cleanup
fi
@@ -231,16 +224,16 @@ echo write
write_hugetlbfs a/b "$MNT"/test2 $size

echo Assert memory charged correctly for child only use.
-assert_state 0 $(($size)) 0 $size
+assert_state $(($size)) $size

rmdir "$CGROUP_ROOT"/a/b
echo Assert memory reparent correctly.
-assert_state 0 $size
+assert_state $size

rm -rf "$MNT"/*
umount "$MNT"
echo Assert memory uncharged correctly.
-assert_state 0 0
+assert_state 0

cleanup

--
2.52.0