linux-kernel - [PATCH 3/3] selftests/mm/charge_reserved_hugetlb: fix hugetlbfs mount size for large hugepages

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Message-ID: <20251220111645.2246009-4-liwang@redhat.com>
Date: Sat, 20 Dec 2025 19:16:45 +0800
From: Li Wang <liwang@...hat.com>
To: linux-kselftest@...r.kernel.org,
	akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Cc: David Hildenbrand <david@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Shuah Khan <shuah@...nel.org>,
	Waiman Long <longman@...hat.com>
Subject: [PATCH 3/3] selftests/mm/charge_reserved_hugetlb: fix hugetlbfs mount size for large hugepages

charge_reserved_hugetlb.sh mounts a hugetlbfs instance at /mnt/huge with
a fixed size of 256M. On systems with large base hugepages (e.g. 512MB),
this is smaller than a single hugepage, so the hugetlbfs mount ends up
with effectively zero capacity (often visible as size=0 in mount output).

As a result, write_to_hugetlbfs fails with ENOMEM and the test can hang
waiting for progress.

--- Error log ---
  # uname -r
  6.12.0-xxx.el10.aarch64+64k

  #./charge_reserved_hugetlb.sh -cgroup-v2
  # -----------------------------------------
  ...
  # nr hugepages = 10
  # writing cgroup limit: 5368709120
  # writing reseravation limit: 5368709120
  ...
  # write_to_hugetlbfs: Error mapping the file: Cannot allocate memory
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  # Waiting for hugetlb memory reservation to reach size 2684354560.
  # 0
  ...

  # mount |grep /mnt/huge
  none on /mnt/huge type hugetlbfs (rw,relatime,seclabel,pagesize=512M,size=0)

  # grep -i huge /proc/meminfo
  ...
  HugePages_Total:      10
  HugePages_Free:       10
  HugePages_Rsvd:        0
  HugePages_Surp:        0
  Hugepagesize:     524288 kB
  Hugetlb:         5242880 kB

Mount hugetlbfs with size=${size}, the number of bytes the test will
reserve/write, so the filesystem capacity is sufficient regardless of
HugeTLB page size.

Signed-off-by: Li Wang <liwang@...hat.com>
Cc: David Hildenbrand <david@...nel.org>
Cc: Mark Brown <broonie@...nel.org>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Waiman Long <longman@...hat.com>
---
 tools/testing/selftests/mm/charge_reserved_hugetlb.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
index 6aa4ce66922c..9deb3dc2cbce 100755
--- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
+++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
@@ -295,7 +295,7 @@ function run_test() {
   setup_cgroup "hugetlb_cgroup_test" "$cgroup_limit" "$reservation_limit"
 
   mkdir -p /mnt/huge
-  mount -t hugetlbfs -o pagesize=${MB}M,size=256M none /mnt/huge
+  mount -t hugetlbfs -o pagesize=${MB}M,size=${size} none /mnt/huge
 
   write_hugetlbfs_and_get_usage "hugetlb_cgroup_test" "$size" "$populate" \
     "$write" "/mnt/huge/test" "$method" "$private" "$expect_failure" \
@@ -349,7 +349,7 @@ function run_multiple_cgroup_test() {
   setup_cgroup "hugetlb_cgroup_test2" "$cgroup_limit2" "$reservation_limit2"
 
   mkdir -p /mnt/huge
-  mount -t hugetlbfs -o pagesize=${MB}M,size=256M none /mnt/huge
+  mount -t hugetlbfs -o pagesize=${MB}M,size=${size} none /mnt/huge
 
   write_hugetlbfs_and_get_usage "hugetlb_cgroup_test1" "$size1" \
     "$populate1" "$write1" "/mnt/huge/test1" "$method" "$private" \
-- 
2.49.0