Re: [PATCH v2 3/4] selftests: mm: implement the mTHP-sized hugepage check helpers

["Zi Yan" <ziy@nvidia.com>]

On Sat Aug 1, 2026 at 2:26 AM EDT, Baolin Wang wrote:
> Implement mTHP-sized hugepage checking helpers using gather_folio_orders().
> Also rename the existing PMD-sized huge page check function to
> __check_pmd_huge() for clarity.
>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>  tools/testing/selftests/mm/vm_util.c | 60 ++++++++++++++++++++++++++--
>  1 file changed, 56 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 09e5d5cabe21..1240d783669c 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -15,6 +15,10 @@
>  #define SMAP_FILE_PATH "/proc/self/smaps"
>  #define STATUS_FILE_PATH "/proc/self/status"
>  #define MAX_LINE_LENGTH 500
> +#define PAGEMAP_PATH "/proc/self/pagemap"
> +#define KPAGEFLAGS_PATH "/proc/kpageflags"
> +#define GET_ORDER(nr_pages)    (31 - __builtin_clz(nr_pages))

This is a fast way of getting log2, but there is no check of the type of
nr_pages. What prevents one using it on a long variable?

At least you can convert nr_pages to unsigned int and add a comment.

> +#define NR_ORDERS 20

Why 20? mTHP orders can only be in [1, pmd_order - 1] and different arch
has different pmd_orders. check_large_folios() probably should just cap
NR_ORDERS at pmd_order.

>  
>  unsigned int __page_size;
>  unsigned int __page_shift;
> @@ -348,7 +352,7 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
>  	return entry;
>  }
>  
> -bool __check_huge(void *addr, char *pattern, int nr_hpages,
> +static bool __check_pmd_huge(void *addr, char *pattern, int nr_hpages,
>  		  uint64_t hpage_size)
>  {
>  	char buffer[MAX_LINE_LENGTH];
> @@ -366,19 +370,67 @@ bool __check_huge(void *addr, char *pattern, int nr_hpages,
>  	return thp == (nr_hpages * (hpage_size >> 10));
>  }
>  
> +static bool check_large_folios(void *addr, unsigned long size, int nr_hpages, uint64_t hpage_size)
> +{
> +	int order = 0, pagesize = getpagesize();
> +	int nr_pages = hpage_size / pagesize;
> +	int pagemap_fd, kpageflags_fd;
> +	int orders[NR_ORDERS], status;

NR_ORDERS is a constant, so you can put orders on stack. I think you can
rename it to MAX_NR_ORDERS, use 20, and check pmd_order is not bigger
than MAX_NR_ORDERS.

> +	bool ret = false;
> +
> +	if (nr_pages > 0)
> +		order = GET_ORDER(nr_pages);

This funciton can fail early if nr_pages is 0.

> +
> +	if (!order || order >= NR_ORDERS)
> +		ksft_exit_fail_msg("invalid order\n");

It should check against pmd_order.

> +
> +	memset(orders, 0, sizeof(int) * NR_ORDERS);
> +	pagemap_fd = open(PAGEMAP_PATH, O_RDONLY);
> +	if (pagemap_fd == -1)
> +		ksft_exit_fail_msg("read pagemap fail\n");
> +
> +	kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY);
> +	if (kpageflags_fd == -1) {
> +		close(pagemap_fd);
> +		ksft_exit_fail_msg("read kpageflags fail\n");
> +	}
> +
> +	status = gather_folio_orders(addr, size, pagemap_fd,
> +			kpageflags_fd, orders, NR_ORDERS);
> +	if (status)
> +		goto out;
> +
> +	if (orders[order] == nr_hpages)
> +		ret = true;
> +
> +out:
> +	close(pagemap_fd);
> +	close(kpageflags_fd);
> +	return ret;
> +}
> +
>  bool check_huge_anon(void *addr, unsigned long size, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
> +	if (hpage_size == read_pmd_pagesize())

read_pmd_pagesize() can fail and return 0. Either you need a check here
or add a ksft_exit_fail_msg() in read_pmd_pagesize() to remove the
burden from all callers.

> +		return __check_pmd_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
> +
> +	return check_large_folios(addr, size, nr_hpages, hpage_size);
>  }
>  
>  bool check_huge_file(void *addr, unsigned long size, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
> +	if (hpage_size == read_pmd_pagesize())
> +		return __check_pmd_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
> +
> +	return check_large_folios(addr, size, nr_hpages, hpage_size);
>  }
>  
>  bool check_huge_shmem(void *addr, unsigned long size, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
> +	if (hpage_size == read_pmd_pagesize())
> +		return __check_pmd_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
> +
> +	return check_large_folios(addr, size, nr_hpages, hpage_size);
>  }
>  
>  int64_t allocate_transhuge(void *ptr, int pagemap_fd)

All read_pmd_pagesize()s above need to be handled.


-- 
Best Regards,
Yan, Zi