Re: [PATCH v9 2/4] kselftest: mm: replace usage of /proc/self/smaps for __check_pmd_huge()

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Thu, Oct 01, 2026 at 10:17:52PM +0100, Yeoreum Yun wrote:
> Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
> glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
> made by memalign().
>
> The underlying VMA may start at a different address from the aligned
> address returned by memalign(). Furthermore, a subsequent
> madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
> already set.
>
> This causes split_huge_page_test to fail because the check_pmd_huge()
> helpers incorrectly require the address returned by memalign() to
> match the VMA start address reported in /proc/self/smaps.
>
> Instead of relying on /proc/self/smaps, use /proc/self/pagemap and
> /proc/kpageflags to detect huge-page mappings checking PAGE_IS_HUGE
> and PAGE_IS_FILE according to type of huge page.
>
> Since shmem pages are also file-backed, simply check whether the page
> is file-backed.
>
> Fixes: 642bc52aed9c ("selftests: vm: bring common functions to a new file")
> Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
> Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>

LGTM so:

Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

Thanks for doing this! :)

> ---
>  tools/testing/selftests/mm/vm_util.c | 78 ++++++++++++++++++++++--------------
>  1 file changed, 49 insertions(+), 29 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index a0ab78ceedb1..a3c3a2706c22 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -351,24 +351,6 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
>  	return entry;
>  }
>
> -static bool __check_pmd_huge(void *addr, char *pattern, int nr_hpages,
> -		  uint64_t hpage_size)
> -{
> -	char buffer[MAX_LINE_LENGTH];
> -	uint64_t thp = -1;
> -	char *entry;
> -
> -	entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer));
> -	if (!entry)
> -		goto err_out;
> -
> -	if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1)
> -		ksft_exit_fail_msg("Reading smap error\n");
> -
> -err_out:
> -	return thp == (nr_hpages * (hpage_size >> 10));
> -}
> -
>  static bool check_large_folios(void *addr, size_t len, int nr_hpages,
>  		uint64_t hpage_size)
>  {
> @@ -410,20 +392,51 @@ static bool check_large_folios(void *addr, size_t len, int nr_hpages,
>  	return ret;
>  }
>
> -bool check_huge_anon(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
> +enum check_huge_type {
> +	CHECK_HUGE_ANON,
> +	CHECK_HUGE_FILE,
> +};
> +
> +static bool check_huge_type(uint64_t categories, enum check_huge_type type)
>  {
> -	uint64_t pmd_pagesize = read_pmd_pagesize();
> +	const bool file = categories & PAGE_IS_FILE;
>
> -	if (!pmd_pagesize)
> -		ksft_exit_fail_msg("reading PMD pagesize failed\n");
> +	switch (type) {
> +	case CHECK_HUGE_ANON:
> +		return !file;
> +	case CHECK_HUGE_FILE:
> +		return file;
> +	}
>
> -	if (hpage_size == pmd_pagesize)
> -		return __check_pmd_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
> +	return false;
> +}
>
> -	return check_large_folios(addr, len, nr_hpages, hpage_size);
> +static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages,
> +		  uint64_t hpage_size, enum check_huge_type type)
> +{
> +	int pagemap_fd;
> +	int nr_pmd_mappings = 0;
> +	uint64_t categories;
> +	char *start = addr;
> +	char *end = start + len;
> +
> +	pagemap_fd = open(PAGEMAP_PATH, O_RDONLY);
> +	if (pagemap_fd < 0)
> +		ksft_exit_fail_perror("open pagemap");
> +
> +	for (; start < end; start += hpage_size) {
> +		categories = pagemap_scan_get_categories(pagemap_fd, start);
> +		if (!(categories & PAGE_IS_HUGE))
> +			continue;
> +		if (check_huge_type(categories, type))
> +			nr_pmd_mappings++;
> +	}
> +	close(pagemap_fd);
> +
> +	return nr_hpages == nr_pmd_mappings;
>  }
>
> -bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
> +bool check_huge_anon(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
>  {
>  	uint64_t pmd_pagesize = read_pmd_pagesize();
>
> @@ -431,12 +444,13 @@ bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
>  		ksft_exit_fail_msg("reading PMD pagesize failed\n");
>
>  	if (hpage_size == pmd_pagesize)
> -		return __check_pmd_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
> +		return __check_pmd_huge(addr, len, nr_hpages, hpage_size,
> +					CHECK_HUGE_ANON);
>
>  	return check_large_folios(addr, len, nr_hpages, hpage_size);
>  }
>
> -bool check_huge_shmem(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
> +bool check_huge_file(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
>  {
>  	uint64_t pmd_pagesize = read_pmd_pagesize();
>
> @@ -444,11 +458,17 @@ bool check_huge_shmem(void *addr, size_t len, int nr_hpages, uint64_t hpage_size
>  		ksft_exit_fail_msg("reading PMD pagesize failed\n");
>
>  	if (hpage_size == pmd_pagesize)
> -		return __check_pmd_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
> +		return __check_pmd_huge(addr, len, nr_hpages, hpage_size,
> +					CHECK_HUGE_FILE);
>
>  	return check_large_folios(addr, len, nr_hpages, hpage_size);
>  }
>
> +bool check_huge_shmem(void *addr, size_t len, int nr_hpages, uint64_t hpage_size)
> +{
> +	return check_huge_file(addr, len, nr_hpages, hpage_size);
> +}
> +
>  int64_t allocate_transhuge(void *ptr, int pagemap_fd)
>  {
>  	uint64_t ent[2];
>
> --
> 2.43.0
>

--
Cheers, Lorenzo