On Fri, Aug 08, 2025 at 03:01:43PM -0400, Zi Yan wrote:
>The helper gathers an folio order statistics of folios within a virtual
>address range and checks it against a given order list. It aims to provide
>a more precise folio order check instead of just checking the existence of
>PMD folios.
>
>Signed-off-by: Zi Yan <[email protected]>
>---
> .../selftests/mm/split_huge_page_test.c | 4 +-
> tools/testing/selftests/mm/vm_util.c | 133 ++++++++++++++++++
> tools/testing/selftests/mm/vm_util.h | 7 +
> 3 files changed, 141 insertions(+), 3 deletions(-)
>
>diff --git a/tools/testing/selftests/mm/split_huge_page_test.c
>b/tools/testing/selftests/mm/split_huge_page_test.c
>index cb364c5670c6..5ab488fab1cd 100644
>--- a/tools/testing/selftests/mm/split_huge_page_test.c
>+++ b/tools/testing/selftests/mm/split_huge_page_test.c
>@@ -34,8 +34,6 @@ uint64_t pmd_pagesize;
> #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
> #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>
>-#define PFN_MASK ((1UL<<55)-1)
>-#define KPF_THP (1UL<<22)
> #define GET_ORDER(nr_pages) (31 - __builtin_clz(nr_pages))
>
> int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>@@ -49,7 +47,7 @@ int is_backed_by_thp(char *vaddr, int pagemap_file, int
>kpageflags_file)
>
> if (kpageflags_file) {
> pread(kpageflags_file, &page_flags, sizeof(page_flags),
>- (paddr & PFN_MASK) * sizeof(page_flags));
>+ PAGEMAP_PFN(paddr) * sizeof(page_flags));
>
is_backed_by_thp() shares similar logic as get_page_flags(), I am thinking we
can
leverage get_page_flags() here.
> return !!(page_flags & KPF_THP);
> }
>diff --git a/tools/testing/selftests/mm/vm_util.c
>b/tools/testing/selftests/mm/vm_util.c
>index 6a239aa413e2..41d50b74b2f6 100644
>--- a/tools/testing/selftests/mm/vm_util.c
>+++ b/tools/testing/selftests/mm/vm_util.c
>@@ -338,6 +338,139 @@ int detect_hugetlb_page_sizes(size_t sizes[], int max)
> return count;
> }
>
>+static int get_page_flags(char *vaddr, int pagemap_file, int kpageflags_file,
>+ uint64_t *flags)
>+{
Nit.
In vm_util.c, we usually name the file descriptor as xxx_fd.
>+ unsigned long pfn;
>+ size_t count;
>+
>+ pfn = pagemap_get_pfn(pagemap_file, vaddr);
>+ /*
>+ * Treat non-present page as a page without any flag, so that
>+ * gather_folio_orders() just record the current folio order.
>+ */
>+ if (pfn == -1UL) {
>+ *flags = 0;
>+ return 0;
>+ }
>+
>+ count = pread(kpageflags_file, flags, sizeof(*flags),
>+ pfn * sizeof(*flags));
>+
>+ if (count != sizeof(*flags))
>+ return -1;
>+
>+ return 0;
>+}
>+
Maybe a simple document here would be helpful.
>+static int gather_folio_orders(char *vaddr_start, size_t len,
>+ int pagemap_file, int kpageflags_file,
>+ int orders[], int nr_orders)
>+{
>+ uint64_t page_flags = 0;
>+ int cur_order = -1;
>+ char *vaddr;
>+
>+ if (!pagemap_file || !kpageflags_file)
>+ return -1;
>+ if (nr_orders <= 0)
>+ return -1;
>+
>+ for (vaddr = vaddr_start; vaddr < vaddr_start + len; ) {
>+ char *next_folio_vaddr;
>+ int status;
>+
>+ if (get_page_flags(vaddr, pagemap_file, kpageflags_file,
>&page_flags))
>+ return -1;
>+
>+ /* all order-0 pages with possible false postive (non folio) */
>+ if (!(page_flags & (KPF_COMPOUND_HEAD | KPF_COMPOUND_TAIL))) {
>+ orders[0]++;
>+ vaddr += psize();
>+ continue;
>+ }
>+
>+ /* skip non thp compound pages */
>+ if (!(page_flags & KPF_THP)) {
>+ vaddr += psize();
>+ continue;
>+ }
>+
>+ /* vpn points to part of a THP at this point */
>+ if (page_flags & KPF_COMPOUND_HEAD)
>+ cur_order = 1;
>+ else {
>+ /* not a head nor a tail in a THP? */
>+ if (!(page_flags & KPF_COMPOUND_TAIL))
>+ return -1;
>+ continue;
>+ }
>+
>+ next_folio_vaddr = vaddr + (1UL << (cur_order + pshift()));
>+
>+ if (next_folio_vaddr >= vaddr_start + len)
>+ break;
Would we skip order 1 folio at the last position?
For example, vaddr_start is 0x2000, len is 0x2000 and the folio at vaddr_start
is an order 1 folio, whose size is exactly 0x2000.
Then we will get next_folio_vaddr == vaddr_start + len.
Could that happen?
>+
>+ while (!(status = get_page_flags(next_folio_vaddr, pagemap_file,
>+ kpageflags_file,
>+ &page_flags))) {
>+ /* next compound head page or order-0 page */
>+ if ((page_flags & KPF_COMPOUND_HEAD) ||
>+ !(page_flags & (KPF_COMPOUND_HEAD |
>+ KPF_COMPOUND_TAIL))) {
Maybe we can put them into one line.
>+ if (cur_order < nr_orders) {
>+ orders[cur_order]++;
>+ cur_order = -1;
>+ vaddr = next_folio_vaddr;
>+ }
>+ break;
>+ }
>+
>+ /* not a head nor a tail in a THP? */
>+ if (!(page_flags & KPF_COMPOUND_TAIL))
>+ return -1;
>+
>+ cur_order++;
>+ next_folio_vaddr = vaddr + (1UL << (cur_order +
>pshift()));
>+ }
The while loop share similar logic as the outer for loop. Is it possible
reduce some duplication?
>+
>+ if (status)
>+ return status;
>+ }
>+ if (cur_order > 0 && cur_order < nr_orders)
>+ orders[cur_order]++;
>+ return 0;
>+}
>+
>+int check_folio_orders(char *vaddr_start, size_t len, int pagemap_file,
>+ int kpageflags_file, int orders[], int nr_orders)
>+{
>+ int *vaddr_orders;
>+ int status;
>+ int i;
>+
>+ vaddr_orders = (int *)malloc(sizeof(int) * nr_orders);
>+
I took a look into thp_setting.h, where defines an array with NR_ORDERS
element which is 20. Maybe we can leverage it here, since we don't expect the
order to be larger.
>+ if (!vaddr_orders)
>+ ksft_exit_fail_msg("Cannot allocate memory for vaddr_orders");
>+
>+ memset(vaddr_orders, 0, sizeof(int) * nr_orders);
>+ status = gather_folio_orders(vaddr_start, len, pagemap_file,
>+ kpageflags_file, vaddr_orders, nr_orders);
>+ if (status)
>+ return status;
>+
>+ status = 0;
>+ for (i = 0; i < nr_orders; i++)
>+ if (vaddr_orders[i] != orders[i]) {
>+ ksft_print_msg("order %d: expected: %d got %d\n", i,
>+ orders[i], vaddr_orders[i]);
>+ status = -1;
>+ }
>+
>+ return status;
>+}
>+
> /* If `ioctls' non-NULL, the allowed ioctls will be returned into the var */
> int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor, uint64_t *ioctls)
>diff --git a/tools/testing/selftests/mm/vm_util.h
>b/tools/testing/selftests/mm/vm_util.h
>index 1843ad48d32b..02e3f1e7065b 100644
>--- a/tools/testing/selftests/mm/vm_util.h
>+++ b/tools/testing/selftests/mm/vm_util.h
>@@ -18,6 +18,11 @@
> #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 +90,8 @@ 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 check_folio_orders(char *vaddr_start, size_t len, int pagemap_file,
>+ int kpageflags_file, int orders[], int nr_orders);
>
> int uffd_register(int uffd, void *addr, uint64_t len,
> bool miss, bool wp, bool minor);
>--
>2.47.2
--
Wei Yang
Help you, Help me
