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) <[email protected]>
> Suggested-by: Zi Yan <[email protected]>
> Signed-off-by: Yeoreum Yun <[email protected]>
> ---
> 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 <[email protected]>
Thanks.
--
Best Regards,
Yan, Zi
