linux-kernel - Re: [PATCH v3 2/3] selftests/mm/charge_reserved

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Message-ID: <94e2d707-94d6-4120-acc8-ee65f91af1c9@redhat.com>
Date: Sun, 21 Dec 2025 15:24:06 -0500
From: Waiman Long <llong@...hat.com>
To: Li Wang <liwang@...hat.com>, akpm@...ux-foundation.org,
 linux-kselftest@...r.kernel.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>
Subject: Re: [PATCH v3 2/3] selftests/mm/charge_reserved_hugetlb: drop mount
 size for hugetlbfs

On 12/21/25 7:26 AM, Li Wang wrote:
> 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 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
>
> Drop the mount args with 'size=256M', so the filesystem capacity is sufficient
> regardless of HugeTLB page size.
>
> Fixes: 29750f71a9 ("hugetlb_cgroup: add hugetlb_cgroup reservation tests")
> 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 e1fe16bcbbe8..fa6713892d82 100755
> --- a/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> +++ b/tools/testing/selftests/mm/charge_reserved_hugetlb.sh
> @@ -290,7 +290,7 @@ 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 none /mnt/huge
>   
>     write_hugetlbfs_and_get_usage "hugetlb_cgroup_test" "$size" "$populate" \
>       "$write" "/mnt/huge/test" "$method" "$private" "$expect_failure" \
> @@ -344,7 +344,7 @@ 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 none /mnt/huge
>   
>     write_hugetlbfs_and_get_usage "hugetlb_cgroup_test1" "$size1" \
>       "$populate1" "$write1" "/mnt/huge/test1" "$method" "$private" \
Acked-by: Waiman Long <longman@...hat.com>