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

[Yeoreum Yun <yeoreum.yun@arm.com>]

On Fri, Sep 25, 2026 at 06:08:44PM +0530, Sarthak Sharma wrote:
> 
> 
> 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

Okay.

> 
> > 
> > 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.

Oops. I'll update.

> 
> > 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.

I see thanks!


> 
> Apart from these nits, rest looks good.
> 
> Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>

-- 
Sincerely,
Yeoreum Yun