Re: [PATCH v8 2/4] kselftest: mm: replace usage of /proc/self/smaps for __check_pmd_huge()

[Sarthak Sharma <sarthak.sharma@arm.com>]

On 9/25/26 12:41 AM, 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 accroding to type of huge page.

s/accroding/according

> 
> Since shmem pages are also file-backed, simply check whether the page
> is file-backed.
> 
> Fixes: 642bc52aed9 ("selftests: vm: bring common functions to a new file")

Checkpatch gives a warning saying it requires atleast 12 characters of
commit SHA.

> Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---

[...]

> +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_msg("open pagemap fail\n");

Can we use ksft_exit_fail_perror("open pagemap") here? Will help in
diagnosing failures as well.

Apart from these nits, rest looks good.

Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>