selftests/mm: reimplement is_backed_by_thp() with more precise check

and rename it to is_backed_by_folio().

is_backed_by_folio() checks if the given vaddr is backed a folio with
a given order. It does so by:
1. getting the pfn of the vaddr;
2. checking kpageflags of the pfn;

if order is greater than 0:
3. checking kpageflags of the head pfn;
4. checking kpageflags of all tail pfns.

pmd_order is added to split_huge_page_test.c and replaces max_order.

[ziy@nvidia.com: reduce code duplication, per David]
  Link: https://lkml.kernel.org/r/F54782D6-65A3-4D35-AE03-8ADE636EE258@nvidia.com
Link: https://lkml.kernel.org/r/20250818184622.1521620-4-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: wang lian <lianux.mm@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
index 3da56feeb944..ab8722f482ae 100644
--- a/tools/testing/selftests/mm/vm_util.h
+++ b/tools/testing/selftests/mm/vm_util.h
@@ -18,6 +18,9 @@
 #define PM_SWAP                       BIT_ULL(62)
 #define PM_PRESENT                    BIT_ULL(63)
 
+#define KPF_COMPOUND_HEAD             BIT_ULL(15)
+#define KPF_COMPOUND_TAIL             BIT_ULL(16)
+#define KPF_THP                       BIT_ULL(22)
 /*
  * Ignore the checkpatch warning, we must read from x but don't want to do
  * anything with it in order to trigger a read page fault. We therefore must use
@@ -85,6 +88,7 @@ bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size);
 int64_t allocate_transhuge(void *ptr, int pagemap_fd);
 unsigned long default_huge_page_size(void);
 int detect_hugetlb_page_sizes(size_t sizes[], int max);
+int pageflags_get(unsigned long pfn, int kpageflags_fd, uint64_t *flags);
 
 int uffd_register(int uffd, void *addr, uint64_t len,
 		  bool miss, bool wp, bool minor);