Re: [PATCH v8 3/4] kselftest: mm: integrate huge page checks

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

On Tue, Sep 29, 2026 at 10:07:37AM +0200, David Hildenbrand (Arm) wrote:
> On 9/24/26 21:11, Yeoreum Yun wrote:
> > check_large_folios() only checks for large folios without distinguishing
> > between anonymous and file-backed huge pages.
> > 
> > To add huge page type checking, integrate the huge page checks into
> > __check_huge():
> > 
> >   1. If hpage_size == pmd_pagesize, check PAGE_IS_HUGE instead of using
> >      check_large_folios(), since only the mapping type matters. This
> >      identifies PMD-mapped huge pages.
> > 
> >   2. Otherwise, use check_large_folios() to detect large folios. This
> >      covers mTHP cases.
> > 
> >   3. Check the folio flags according to the huge page type.
> > 
> > Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
> > Suggested-by: Zi Yan <ziy@nvidia.com>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
> 
> Instead of merging both things (detecting mapping vs. detecting anon vs. file),
> could we simply perform the anon vs. file change separately?
> 
> Doing another pagemap walk that focuses on that should end up with something
> that is easier to read.

Okay. I'll change like below in next-spin:

-------&<-------

@@ -411,57 +400,78 @@ static bool check_huge_type(uint64_t categories, enum check_huge_type type)
        return false;
 }

-static bool __check_pmd_huge(void *addr, size_t len, int nr_hpages,
-                 uint64_t hpage_size, enum check_huge_type type)
+static bool __check_huge(void *addr, size_t len, int nr_hpages,
+               uint64_t hpage_size, enum check_huge_type type)
 {
 {
-       int pagemap_fd;
+       bool ret = false;
+       int pagemap_fd, kpageflags_fd;
        int nr_pmd_mappings = 0;
+       uint64_t pmd_pagesize, scan_mapping_size;
        uint64_t categories;
+       unsigned long pfn;
+       bool check_pmd_mapping, allow_nonpresent;
        char *start = addr;
        char *end = start + len;

+       pmd_pagesize = read_pmd_pagesize();
+       if (!pmd_pagesize)
+               ksft_exit_fail_msg("reading PMD pagesize failed\n");
+
+       check_pmd_mapping = hpage_size == pmd_pagesize;
+       scan_mapping_size = (nr_hpages > 0) ? hpage_size : psize();
+       /* Some mTHP tests check a partially populated PMD-sized range. */
+       allow_nonpresent = (uint64_t)nr_hpages * hpage_size < len;
+
        pagemap_fd = open(PAGEMAP_PATH, O_RDONLY);
        if (pagemap_fd < 0)
                ksft_exit_fail_perror("open pagemap");

-       for (; start < end; start += hpage_size) {
+       kpageflags_fd = open(KPAGEFLAGS_PATH, O_RDONLY);
+       if (kpageflags_fd < 0)
+               ksft_exit_fail_perror("open kpageflags");
+
+       for (; start < end; start += scan_mapping_size) {
                categories = pagemap_scan_get_categories(pagemap_fd, start);
-               if (!(categories & PAGE_IS_HUGE))
+               pfn = pagemap_get_pfn(pagemap_fd, start);
+               if (pfn == -1UL) {
+                       if (!allow_nonpresent)
+                               goto out;
                        continue;
-               if (check_huge_type(categories, type))
+               }
+               if (!check_huge_type(categories, type))
+                       goto out;
+       }
+
+       if (!check_pmd_mapping) {
+               ret = check_large_folios(pagemap_fd, kpageflags_fd,
+                               addr, len, nr_hpages, hpage_size);
+               goto out;
+       }
+
+       for (start = addr; start < end; start += scan_mapping_size) {
+               categories = pagemap_scan_get_categories(pagemap_fd, start);
+               if (categories & PAGE_IS_HUGE)
                        nr_pmd_mappings++;
        }
-       close(pagemap_fd);

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

-- 
Sincerely,
Yeoreum Yun