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, 2 insertions, 2 deletions

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 4362021b1ce7..c54177aabebd 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -1086,7 +1086,7 @@ debug_vm_pgtable_alloc_huge_page(struct pgtable_debug_args *args, int order)
 	struct page *page = NULL;
 
 #ifdef CONFIG_CONTIG_ALLOC
-	if (order >= MAX_ORDER) {
+	if (order > MAX_ORDER) {
 		page = alloc_contig_pages((1 << order), GFP_KERNEL,
 					  first_online_node, NULL);
 		if (page) {
@@ -1096,7 +1096,7 @@ debug_vm_pgtable_alloc_huge_page(struct pgtable_debug_args *args, int order)
 	}
 #endif
 
-	if (order < MAX_ORDER)
+	if (order <= MAX_ORDER)
 		page = alloc_pages(GFP_KERNEL, order);
 
 	return page;