Re: [PATCH v3 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

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

On Fri Aug 28, 2026 at 4:11 AM EDT, 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_huge_xxx()
> helpers incorrectly require the address returned by memalign() to
> match the VMA start address reported in /proc/self/smaps.
>
> Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
> /proc/self/smaps to detect huge pages.
>
> Reported-by: David Hildenbrand (Arm) <david@kernel.org>
> Suggested-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  tools/testing/selftests/mm/vm_util.c | 145 ++++++++++++++++++++++-------------
>  tools/testing/selftests/mm/vm_util.h |   1 +
>  2 files changed, 92 insertions(+), 54 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 4821a3563036..083b72d92b14 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -351,31 +351,13 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
>  	return entry;
>  }
>  

<snip>

> +	for (; start < end; start += scan_mapping_size) {
> +		categories = pagemap_scan_get_categories(pagemap_fd, start);
> +		pfn = pagemap_get_pfn(pagemap_fd, start);
> +		if (pfn == -1UL) {
> +			if (!allow_nonpresent)
> +				goto out;
> +			else
> +				continue;
> +		}
> +		if (pageflags_get(pfn, kpageflags_fd, &kpf))
> +			ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
> +		if (check_pmd_mapping && (categories & PAGE_IS_HUGE))
> +			nr_pmd_mappings++;
> +		if (kpf & KPF_COMPOUND_TAIL)
> +			continue;
> +		if (!check_huge_type(categories, kpf, type))
> +			goto out;
> +	}
> +	

There is a trailing tab.

> +	if (check_pmd_mapping && (nr_pmd_mappings != nr_hpages))
> +		goto out;
> +	ret = true;
> +
> +out:
> +	close(pagemap_fd);
> +	close(kpageflags_fd);
> +	return ret;
>  }
>  

Otherwise, LGTM. I assume the replacement of memalign(), from the
discussion between you and Lorenzo, will be added in a separate patch.
For this patch,

Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks.

-- 
Best Regards,
Yan, Zi