[PATCH v2] docs: pagemap: fix flags location, member name and sample code

[Zenghui Yu <zenghui.yu@linux.dev>]

The userland visible page flags (KPF_*) were initially moved to
include/linux/kernel-page-flags.h in commit 1a9b5b7fe0c5 ("mm: export
stable page flags"), and later moved to
include/uapi/linux/kernel-page-flags.h in commit 607ca46e97a1 ("UAPI:
(Scripted) Disintegrate include/linux").  Update the doc to reflect the
current location of these flags.

The member @walk_end of struct pm_scan_arg {} was wrongly written as
"end_walk".

The first sample code of the PAGEMAP_SCAN ioctl wrongly used the
PM_SCAN_CHECK_WPASYNC flag twice, instead of the PM_SCAN_WP_MATCHING flag.
The second one included the wrong category in the required mask -
PAGE_IS_FILE should be used instead of PAGE_IS_SWAPPED as per the
intention.

Fix them all together.

Signed-off-by: Zenghui Yu <zenghui.yu@linux.dev>
---

* From v1 [1]:
  - drop PAGE_IS_SWAPPED in .category_mask (David)
  - fix typo in commit message (David)
  - didn't collect SeongJae's R-b (as the content has changed anyway) but
    thank you for that!

[1] https://lore.kernel.org/20260625174447.24292-1-zenghui.yu@linux.dev

 Documentation/admin-guide/mm/pagemap.rst | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst
index c57e61b5d8aa..20e3fe76f099 100644
--- a/Documentation/admin-guide/mm/pagemap.rst
+++ b/Documentation/admin-guide/mm/pagemap.rst
@@ -67,7 +67,7 @@ number of times a page is mapped.
  * ``/proc/kpageflags``.  This file contains a 64-bit set of flags for each
    page, indexed by PFN.
 
-   The flags are (from ``fs/proc/page.c``, above kpageflags_read):
+   The flags are (from ``include/uapi/linux/kernel-page-flags.h``):
 
     0. LOCKED
     1. ERROR
@@ -264,7 +264,7 @@ The ``struct pm_scan_arg`` is used as the argument of the IOCTL.
     provided or not.
  3. The range is specified through ``start`` and ``end``.
  4. The walk can abort before visiting the complete range such as the user buffer
-    can get full etc. The walk ending address is specified in``end_walk``.
+    can get full etc. The walk ending address is specified in ``walk_end``.
  5. The output buffer of ``struct page_region`` array and size is specified in
     ``vec`` and ``vec_len``.
  6. The optional maximum requested pages are specified in the ``max_pages``.
@@ -275,7 +275,7 @@ Find pages which have been written and WP them as well::
 
    struct pm_scan_arg arg = {
    .size = sizeof(arg),
-   .flags = PM_SCAN_CHECK_WPASYNC | PM_SCAN_CHECK_WPASYNC,
+   .flags = PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC,
    ..
    .category_mask = PAGE_IS_WRITTEN,
    .return_mask = PAGE_IS_WRITTEN,
@@ -288,7 +288,7 @@ present or huge::
    .size = sizeof(arg),
    .flags = 0,
    ..
-   .category_mask = PAGE_IS_WRITTEN | PAGE_IS_SWAPPED,
+   .category_mask = PAGE_IS_WRITTEN | PAGE_IS_FILE,
    .category_inverted = PAGE_IS_SWAPPED,
    .category_anyof_mask = PAGE_IS_PRESENT | PAGE_IS_HUGE,
    .return_mask = PAGE_IS_WRITTEN | PAGE_IS_SWAPPED |
-- 
2.53.0