mm, treewide: redefine MAX_ORDER sanely

MAX_ORDER currently defined as number of orders page allocator supports:
user can ask buddy allocator for page order between 0 and MAX_ORDER-1.

This definition is counter-intuitive and lead to number of bugs all over
the kernel.

Change the definition of MAX_ORDER to be inclusive: the range of orders
user can ask from buddy allocator is 0..MAX_ORDER now.

[[email protected]: fix min() warning]
  Link: https://lkml.kernel.org/r/20230315153800.32wib3n5rickolvh@box
[[email protected]: fix another min_t warning]
[[email protected]: fixups per Zi Yan]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: fix underlining in docs]
  Link: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Michael Ellerman <[email protected]>	[powerpc]
Cc: "Kirill A. Shutemov" <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8faac4310cb5..98719e72b5e2 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7002,7 +7002,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 	 * scan_control uses s8 fields for order, priority, and reclaim_idx.
 	 * Confirm they are large enough for max values.
 	 */
-	BUILD_BUG_ON(MAX_ORDER > S8_MAX);
+	BUILD_BUG_ON(MAX_ORDER >= S8_MAX);
 	BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
 	BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);