Re: [PATCH v3 2/3] selftests/mm/charge_reserved_hugetlb: drop mount size for hugetlbfs

David Hildenbrand (Red Hat)
2025-12-22T10:01:24Z

On 12/21/25 13:26, 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")

Likely Andrew should add a CC of stable

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

--
Cheers

David