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

[Yeoreum Yun]

On Fri, Aug 28, 2026 at 11:13:00AM -0400, Zi Yan wrote:
> 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@xxxxxxxxxx>
> > Suggested-by: Zi Yan <ziy@xxxxxxxxxx>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>
> > ---
> >  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,

Yeap. I'll post with the separated one.

> 
> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>

Thanks!

-- 
Sincerely,
Yeoreum Yun