diff mbox series

[1/2] mm, treewide: Introduce NR_PAGE_ORDERS

Message ID 20231121122712.31339-1-kirill.shutemov@linux.intel.com (mailing list archive)
State New, archived
Headers show
Series [1/2] mm, treewide: Introduce NR_PAGE_ORDERS | expand

Commit Message

Kirill A . Shutemov Nov. 21, 2023, 12:27 p.m. UTC
NR_PAGE_ORDERS defines the number of page orders supported by the page
allocator, ranging from 0 to MAX_ORDER, MAX_ORDER + 1 in total.

NR_PAGE_ORDERS assists in defining arrays of page orders and allows for
more natural iteration over them.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 .../admin-guide/kdump/vmcoreinfo.rst          |  4 ++--
 arch/arm64/kvm/hyp/include/nvhe/gfp.h         |  2 +-
 arch/sparc/kernel/traps_64.c                  |  2 +-
 drivers/gpu/drm/ttm/tests/ttm_device_test.c   |  2 +-
 drivers/gpu/drm/ttm/ttm_pool.c                | 20 +++++++++----------
 include/drm/ttm/ttm_pool.h                    |  2 +-
 include/linux/mmzone.h                        |  6 ++++--
 kernel/crash_core.c                           |  2 +-
 lib/test_meminit.c                            |  2 +-
 mm/compaction.c                               |  2 +-
 mm/kmsan/init.c                               |  2 +-
 mm/page_alloc.c                               | 13 ++++++------
 mm/page_reporting.c                           |  2 +-
 mm/show_mem.c                                 |  8 ++++----
 mm/vmstat.c                                   | 12 +++++------
 15 files changed, 41 insertions(+), 40 deletions(-)

Comments

Linus Torvalds Nov. 21, 2023, 5:46 p.m. UTC | #1
On Tue, 21 Nov 2023 at 04:27, Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> NR_PAGE_ORDERS defines the number of page orders supported by the page
> allocator, ranging from 0 to MAX_ORDER, MAX_ORDER + 1 in total.
>
> NR_PAGE_ORDERS assists in defining arrays of page orders and allows for
> more natural iteration over them.

These two patches look much better to me, but I think you missed one area.

Most of the Kconfig changes by commit 23baf831a32c ("mm, treewide:
redefine MAX_ORDER sanely") should also be basically reverted to use
this new NR_PAGE_ORDERS.

IOW, I think the ARCH_FORCE_MAX_ORDER #defines etc should also be done
in "number of page orders". I suspect from a documentation standpoint
that also makes more sense in places, eg I think that right now your
patch says

                        amount of memory for normal system use. The maximum
-                       possible value is MAX_ORDER/2.  Setting this parameter
+                       possible value is MAX_PAGE_ORDER/2.  Setting this

and that's actually nonsensical, because it's NR_PAGE_ORDERS that was
at least historically the boundary (and historically the one that was
an even number that can be halved cleanly).

So that kernel parameter should be in terms of NR_PAGE_ORDERS.

But yes, I do think the naming now makes more sense, so other than
that reaction I think these changes are good.

                  Linus
Kirill A . Shutemov Nov. 22, 2023, 12:34 p.m. UTC | #2
On Tue, Nov 21, 2023 at 09:46:57AM -0800, Linus Torvalds wrote:
> On Tue, 21 Nov 2023 at 04:27, Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com> wrote:
> >
> > NR_PAGE_ORDERS defines the number of page orders supported by the page
> > allocator, ranging from 0 to MAX_ORDER, MAX_ORDER + 1 in total.
> >
> > NR_PAGE_ORDERS assists in defining arrays of page orders and allows for
> > more natural iteration over them.
> 
> These two patches look much better to me, but I think you missed one area.
> 
> Most of the Kconfig changes by commit 23baf831a32c ("mm, treewide:
> redefine MAX_ORDER sanely") should also be basically reverted to use
> this new NR_PAGE_ORDERS.

I am not convinced.

Some architectures make this option user-visible and, in my view, user
cares more about the largest page size buddy allocator can provide than
size of the array inside the allocator.

> IOW, I think the ARCH_FORCE_MAX_ORDER #defines etc should also be done
> in "number of page orders". I suspect from a documentation standpoint
> that also makes more sense in places, eg I think that right now your
> patch says
> 
>                         amount of memory for normal system use. The maximum
> -                       possible value is MAX_ORDER/2.  Setting this parameter
> +                       possible value is MAX_PAGE_ORDER/2.  Setting this
> 
> and that's actually nonsensical, because it's NR_PAGE_ORDERS that was
> at least historically the boundary (and historically the one that was
> an even number that can be halved cleanly).

Maybe historically (I didn't check), but not now. It is all over the
place. And it more even in MAX_PAGE_ORDER terms than in NR_PAGE_ORDERS:

arch/arc/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/arc/Kconfig-	int "Maximum zone order"
arch/arc/Kconfig-	default "11" if ARC_HUGEPAGE_16M
arch/arc/Kconfig-	default "10"
--
arch/arm/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/arm/Kconfig-	int "Order of maximal physically contiguous allocations"
arch/arm/Kconfig-	default "11" if SOC_AM33XX
arch/arm/Kconfig-	default "8" if SA1111
arch/arm/Kconfig-	default "10"
--
arch/arm64/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/arm64/Kconfig-	int
arch/arm64/Kconfig-	default "13" if ARM64_64K_PAGES
arch/arm64/Kconfig-	default "11" if ARM64_16K_PAGES
arch/arm64/Kconfig-	default "10"
--
arch/loongarch/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/loongarch/Kconfig-	int "Maximum zone order"
arch/loongarch/Kconfig-	default "13" if PAGE_SIZE_64KB
arch/loongarch/Kconfig-	default "11" if PAGE_SIZE_16KB
arch/loongarch/Kconfig-	default "10"
--
arch/m68k/Kconfig.cpu:config ARCH_FORCE_MAX_ORDER
arch/m68k/Kconfig.cpu-	int "Order of maximal physically contiguous allocations" if ADVANCED
arch/m68k/Kconfig.cpu-	depends on !SINGLE_MEMORY_CHUNK
arch/m68k/Kconfig.cpu-	default "10"
--
arch/mips/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/mips/Kconfig-	int "Maximum zone order"
arch/mips/Kconfig-	default "13" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_64KB
arch/mips/Kconfig-	default "12" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_32KB
arch/mips/Kconfig-	default "11" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_16KB
arch/mips/Kconfig-	default "10"
--
arch/nios2/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/nios2/Kconfig-	int "Order of maximal physically contiguous allocations"
arch/nios2/Kconfig-	default "10"
--
arch/powerpc/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/powerpc/Kconfig-	int "Order of maximal physically contiguous allocations"
arch/powerpc/Kconfig-	range 7 8 if PPC64 && PPC_64K_PAGES
arch/powerpc/Kconfig-	default "8" if PPC64 && PPC_64K_PAGES
arch/powerpc/Kconfig-	range 12 12 if PPC64 && !PPC_64K_PAGES
arch/powerpc/Kconfig-	default "12" if PPC64 && !PPC_64K_PAGES
arch/powerpc/Kconfig-	range 8 10 if PPC32 && PPC_16K_PAGES
arch/powerpc/Kconfig-	default "8" if PPC32 && PPC_16K_PAGES
arch/powerpc/Kconfig-	range 6 10 if PPC32 && PPC_64K_PAGES
arch/powerpc/Kconfig-	default "6" if PPC32 && PPC_64K_PAGES
arch/powerpc/Kconfig-	range 4 10 if PPC32 && PPC_256K_PAGES
--
arch/sh/mm/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/sh/mm/Kconfig-	int "Order of maximal physically contiguous allocations"
arch/sh/mm/Kconfig-	default "8" if PAGE_SIZE_16KB
arch/sh/mm/Kconfig-	default "6" if PAGE_SIZE_64KB
arch/sh/mm/Kconfig-	default "13" if !MMU
arch/sh/mm/Kconfig-	default "10"
--
arch/sparc/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/sparc/Kconfig-	int "Order of maximal physically contiguous allocations"
arch/sparc/Kconfig-	default "12"
--
arch/xtensa/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/xtensa/Kconfig-	int "Order of maximal physically contiguous allocations"
arch/xtensa/Kconfig-	default "10"
Kirill A . Shutemov Dec. 5, 2023, 1:03 a.m. UTC | #3
On Wed, Nov 22, 2023 at 03:34:13PM +0300, Kirill A. Shutemov wrote:
> On Tue, Nov 21, 2023 at 09:46:57AM -0800, Linus Torvalds wrote:
> > On Tue, 21 Nov 2023 at 04:27, Kirill A. Shutemov
> > <kirill.shutemov@linux.intel.com> wrote:
> > >
> > > NR_PAGE_ORDERS defines the number of page orders supported by the page
> > > allocator, ranging from 0 to MAX_ORDER, MAX_ORDER + 1 in total.
> > >
> > > NR_PAGE_ORDERS assists in defining arrays of page orders and allows for
> > > more natural iteration over them.
> > 
> > These two patches look much better to me, but I think you missed one area.
> > 
> > Most of the Kconfig changes by commit 23baf831a32c ("mm, treewide:
> > redefine MAX_ORDER sanely") should also be basically reverted to use
> > this new NR_PAGE_ORDERS.
> 
> I am not convinced.
> 
> Some architectures make this option user-visible and, in my view, user
> cares more about the largest page size buddy allocator can provide than
> size of the array inside the allocator.
> 
> > IOW, I think the ARCH_FORCE_MAX_ORDER #defines etc should also be done
> > in "number of page orders". I suspect from a documentation standpoint
> > that also makes more sense in places, eg I think that right now your
> > patch says
> > 
> >                         amount of memory for normal system use. The maximum
> > -                       possible value is MAX_ORDER/2.  Setting this parameter
> > +                       possible value is MAX_PAGE_ORDER/2.  Setting this
> > 
> > and that's actually nonsensical, because it's NR_PAGE_ORDERS that was
> > at least historically the boundary (and historically the one that was
> > an even number that can be halved cleanly).
> 
> Maybe historically (I didn't check), but not now. It is all over the
> place. And it more even in MAX_PAGE_ORDER terms than in NR_PAGE_ORDERS:
> 
> ...

Ping?
diff mbox series

Patch

diff --git a/Documentation/admin-guide/kdump/vmcoreinfo.rst b/Documentation/admin-guide/kdump/vmcoreinfo.rst
index 78e4d2e7ba14..766b47ad8fb4 100644
--- a/Documentation/admin-guide/kdump/vmcoreinfo.rst
+++ b/Documentation/admin-guide/kdump/vmcoreinfo.rst
@@ -172,7 +172,7 @@  variables.
 Offset of the free_list's member. This value is used to compute the number
 of free pages.
 
-Each zone has a free_area structure array called free_area[MAX_ORDER + 1].
+Each zone has a free_area structure array called free_area[NR_PAGE_ORDERS].
 The free_list represents a linked list of free page blocks.
 
 (list_head, next|prev)
@@ -189,7 +189,7 @@  Offsets of the vmap_area's members. They carry vmalloc-specific
 information. Makedumpfile gets the start address of the vmalloc region
 from this.
 
-(zone.free_area, MAX_ORDER + 1)
+(zone.free_area, NR_PAGE_ORDERS)
 -------------------------------
 
 Free areas descriptor. User-space tools use this value to iterate the
diff --git a/arch/arm64/kvm/hyp/include/nvhe/gfp.h b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
index fe5472a184a3..97c527ef53c2 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/gfp.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
@@ -16,7 +16,7 @@  struct hyp_pool {
 	 * API at EL2.
 	 */
 	hyp_spinlock_t lock;
-	struct list_head free_area[MAX_ORDER + 1];
+	struct list_head free_area[NR_PAGE_ORDERS];
 	phys_addr_t range_start;
 	phys_addr_t range_end;
 	unsigned short max_order;
diff --git a/arch/sparc/kernel/traps_64.c b/arch/sparc/kernel/traps_64.c
index 08ffd17d5ec3..523a6e5ee925 100644
--- a/arch/sparc/kernel/traps_64.c
+++ b/arch/sparc/kernel/traps_64.c
@@ -897,7 +897,7 @@  void __init cheetah_ecache_flush_init(void)
 
 	/* Now allocate error trap reporting scoreboard. */
 	sz = NR_CPUS * (2 * sizeof(struct cheetah_err_info));
-	for (order = 0; order <= MAX_ORDER; order++) {
+	for (order = 0; order < NR_PAGE_ORDERS; order++) {
 		if ((PAGE_SIZE << order) >= sz)
 			break;
 	}
diff --git a/drivers/gpu/drm/ttm/tests/ttm_device_test.c b/drivers/gpu/drm/ttm/tests/ttm_device_test.c
index b1b423b68cdf..19eaff22e6ae 100644
--- a/drivers/gpu/drm/ttm/tests/ttm_device_test.c
+++ b/drivers/gpu/drm/ttm/tests/ttm_device_test.c
@@ -175,7 +175,7 @@  static void ttm_device_init_pools(struct kunit *test)
 
 	if (params->pools_init_expected) {
 		for (int i = 0; i < TTM_NUM_CACHING_TYPES; ++i) {
-			for (int j = 0; j <= MAX_ORDER; ++j) {
+			for (int j = 0; j < NR_PAGE_ORDERS; ++j) {
 				pt = pool->caching[i].orders[j];
 				KUNIT_EXPECT_PTR_EQ(test, pt.pool, pool);
 				KUNIT_EXPECT_EQ(test, pt.caching, i);
diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index fe610a3cace0..d183bb97c526 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -65,11 +65,11 @@  module_param(page_pool_size, ulong, 0644);
 
 static atomic_long_t allocated_pages;
 
-static struct ttm_pool_type global_write_combined[MAX_ORDER + 1];
-static struct ttm_pool_type global_uncached[MAX_ORDER + 1];
+static struct ttm_pool_type global_write_combined[NR_PAGE_ORDERS];
+static struct ttm_pool_type global_uncached[NR_PAGE_ORDERS];
 
-static struct ttm_pool_type global_dma32_write_combined[MAX_ORDER + 1];
-static struct ttm_pool_type global_dma32_uncached[MAX_ORDER + 1];
+static struct ttm_pool_type global_dma32_write_combined[NR_PAGE_ORDERS];
+static struct ttm_pool_type global_dma32_uncached[NR_PAGE_ORDERS];
 
 static spinlock_t shrinker_lock;
 static struct list_head shrinker_list;
@@ -568,7 +568,7 @@  void ttm_pool_init(struct ttm_pool *pool, struct device *dev,
 
 	if (use_dma_alloc || nid != NUMA_NO_NODE) {
 		for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
-			for (j = 0; j <= MAX_ORDER; ++j)
+			for (j = 0; j < NR_PAGE_ORDERS; ++j)
 				ttm_pool_type_init(&pool->caching[i].orders[j],
 						   pool, i, j);
 	}
@@ -601,7 +601,7 @@  void ttm_pool_fini(struct ttm_pool *pool)
 
 	if (pool->use_dma_alloc || pool->nid != NUMA_NO_NODE) {
 		for (i = 0; i < TTM_NUM_CACHING_TYPES; ++i)
-			for (j = 0; j <= MAX_ORDER; ++j)
+			for (j = 0; j < NR_PAGE_ORDERS; ++j)
 				ttm_pool_type_fini(&pool->caching[i].orders[j]);
 	}
 
@@ -656,7 +656,7 @@  static void ttm_pool_debugfs_header(struct seq_file *m)
 	unsigned int i;
 
 	seq_puts(m, "\t ");
-	for (i = 0; i <= MAX_ORDER; ++i)
+	for (i = 0; i < NR_PAGE_ORDERS; ++i)
 		seq_printf(m, " ---%2u---", i);
 	seq_puts(m, "\n");
 }
@@ -667,7 +667,7 @@  static void ttm_pool_debugfs_orders(struct ttm_pool_type *pt,
 {
 	unsigned int i;
 
-	for (i = 0; i <= MAX_ORDER; ++i)
+	for (i = 0; i < NR_PAGE_ORDERS; ++i)
 		seq_printf(m, " %8u", ttm_pool_type_count(&pt[i]));
 	seq_puts(m, "\n");
 }
@@ -776,7 +776,7 @@  int ttm_pool_mgr_init(unsigned long num_pages)
 	spin_lock_init(&shrinker_lock);
 	INIT_LIST_HEAD(&shrinker_list);
 
-	for (i = 0; i <= MAX_ORDER; ++i) {
+	for (i = 0; i < NR_PAGE_ORDERS; ++i) {
 		ttm_pool_type_init(&global_write_combined[i], NULL,
 				   ttm_write_combined, i);
 		ttm_pool_type_init(&global_uncached[i], NULL, ttm_uncached, i);
@@ -816,7 +816,7 @@  void ttm_pool_mgr_fini(void)
 {
 	unsigned int i;
 
-	for (i = 0; i <= MAX_ORDER; ++i) {
+	for (i = 0; i < NR_PAGE_ORDERS; ++i) {
 		ttm_pool_type_fini(&global_write_combined[i]);
 		ttm_pool_type_fini(&global_uncached[i]);
 
diff --git a/include/drm/ttm/ttm_pool.h b/include/drm/ttm/ttm_pool.h
index 30a347e5aa11..4490d43c63e3 100644
--- a/include/drm/ttm/ttm_pool.h
+++ b/include/drm/ttm/ttm_pool.h
@@ -74,7 +74,7 @@  struct ttm_pool {
 	bool use_dma32;
 
 	struct {
-		struct ttm_pool_type orders[MAX_ORDER + 1];
+		struct ttm_pool_type orders[NR_PAGE_ORDERS];
 	} caching[TTM_NUM_CACHING_TYPES];
 };
 
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 3c25226beeed..1c2829ed8348 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -34,6 +34,8 @@ 
 
 #define IS_MAX_ORDER_ALIGNED(pfn) IS_ALIGNED(pfn, MAX_ORDER_NR_PAGES)
 
+#define NR_PAGE_ORDERS (MAX_ORDER + 1)
+
 /*
  * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed
  * costly to service.  That is between allocation orders which should
@@ -95,7 +97,7 @@  static inline bool migratetype_is_mergeable(int mt)
 }
 
 #define for_each_migratetype_order(order, type) \
-	for (order = 0; order <= MAX_ORDER; order++) \
+	for (order = 0; order < NR_PAGE_ORDERS; order++) \
 		for (type = 0; type < MIGRATE_TYPES; type++)
 
 extern int page_group_by_mobility_disabled;
@@ -943,7 +945,7 @@  struct zone {
 	CACHELINE_PADDING(_pad1_);
 
 	/* free areas of different sizes */
-	struct free_area	free_area[MAX_ORDER + 1];
+	struct free_area	free_area[NR_PAGE_ORDERS];
 
 #ifdef CONFIG_UNACCEPTED_MEMORY
 	/* Pages to be accepted. All pages on the list are MAX_ORDER */
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index efe87d501c8c..08ba6e95492b 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -802,7 +802,7 @@  static int __init crash_save_vmcoreinfo_init(void)
 	VMCOREINFO_OFFSET(list_head, prev);
 	VMCOREINFO_OFFSET(vmap_area, va_start);
 	VMCOREINFO_OFFSET(vmap_area, list);
-	VMCOREINFO_LENGTH(zone.free_area, MAX_ORDER + 1);
+	VMCOREINFO_LENGTH(zone.free_area, NR_PAGE_ORDERS);
 	log_buf_vmcoreinfo_setup();
 	VMCOREINFO_LENGTH(free_area.free_list, MIGRATE_TYPES);
 	VMCOREINFO_NUMBER(NR_FREE_PAGES);
diff --git a/lib/test_meminit.c b/lib/test_meminit.c
index 0ae35223d773..0dc173849a54 100644
--- a/lib/test_meminit.c
+++ b/lib/test_meminit.c
@@ -93,7 +93,7 @@  static int __init test_pages(int *total_failures)
 	int failures = 0, num_tests = 0;
 	int i;
 
-	for (i = 0; i <= MAX_ORDER; i++)
+	for (i = 0; i < NR_PAGE_ORDERS; i++)
 		num_tests += do_alloc_pages_order(i, &failures);
 
 	REPORT_FAILURES_IN_FN();
diff --git a/mm/compaction.c b/mm/compaction.c
index 01ba298739dd..6c8378653cb6 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2226,7 +2226,7 @@  static enum compact_result __compact_finished(struct compact_control *cc)
 
 	/* Direct compactor: Is a suitable page free? */
 	ret = COMPACT_NO_SUITABLE_PAGE;
-	for (order = cc->order; order <= MAX_ORDER; order++) {
+	for (order = cc->order; order < NR_PAGE_ORDERS; order++) {
 		struct free_area *area = &cc->zone->free_area[order];
 		bool can_steal;
 
diff --git a/mm/kmsan/init.c b/mm/kmsan/init.c
index ffedf4dbc49d..103e2e88ea03 100644
--- a/mm/kmsan/init.c
+++ b/mm/kmsan/init.c
@@ -96,7 +96,7 @@  void __init kmsan_init_shadow(void)
 struct metadata_page_pair {
 	struct page *shadow, *origin;
 };
-static struct metadata_page_pair held_back[MAX_ORDER + 1] __initdata;
+static struct metadata_page_pair held_back[NR_PAGE_ORDERS] __initdata;
 
 /*
  * Eager metadata allocation. When the memblock allocator is freeing pages to
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 733732e7e0ba..8a9082a725ee 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1571,7 +1571,7 @@  struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 	struct page *page;
 
 	/* Find a page of the appropriate size in the preferred list */
-	for (current_order = order; current_order <= MAX_ORDER; ++current_order) {
+	for (current_order = order; current_order < NR_PAGE_ORDERS; ++current_order) {
 		area = &(zone->free_area[current_order]);
 		page = get_page_from_free_area(area, migratetype);
 		if (!page)
@@ -1941,7 +1941,7 @@  static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
 			continue;
 
 		spin_lock_irqsave(&zone->lock, flags);
-		for (order = 0; order <= MAX_ORDER; order++) {
+		for (order = 0; order < NR_PAGE_ORDERS; order++) {
 			struct free_area *area = &(zone->free_area[order]);
 
 			page = get_page_from_free_area(area, MIGRATE_HIGHATOMIC);
@@ -2051,8 +2051,7 @@  __rmqueue_fallback(struct zone *zone, int order, int start_migratetype,
 	return false;
 
 find_smallest:
-	for (current_order = order; current_order <= MAX_ORDER;
-							current_order++) {
+	for (current_order = order; current_order < NR_PAGE_ORDERS; current_order++) {
 		area = &(zone->free_area[current_order]);
 		fallback_mt = find_suitable_fallback(area, current_order,
 				start_migratetype, false, &can_steal);
@@ -3007,7 +3006,7 @@  bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 		return true;
 
 	/* For a high-order request, check at least one suitable page is free */
-	for (o = order; o <= MAX_ORDER; o++) {
+	for (o = order; o < NR_PAGE_ORDERS; o++) {
 		struct free_area *area = &z->free_area[o];
 		int mt;
 
@@ -6635,7 +6634,7 @@  bool is_free_buddy_page(struct page *page)
 	unsigned long pfn = page_to_pfn(page);
 	unsigned int order;
 
-	for (order = 0; order <= MAX_ORDER; order++) {
+	for (order = 0; order < NR_PAGE_ORDERS; order++) {
 		struct page *page_head = page - (pfn & ((1 << order) - 1));
 
 		if (PageBuddy(page_head) &&
@@ -6690,7 +6689,7 @@  bool take_page_off_buddy(struct page *page)
 	bool ret = false;
 
 	spin_lock_irqsave(&zone->lock, flags);
-	for (order = 0; order <= MAX_ORDER; order++) {
+	for (order = 0; order < NR_PAGE_ORDERS; order++) {
 		struct page *page_head = page - (pfn & ((1 << order) - 1));
 		int page_order = buddy_order(page_head);
 
diff --git a/mm/page_reporting.c b/mm/page_reporting.c
index b021f482a4cb..66369cc5279b 100644
--- a/mm/page_reporting.c
+++ b/mm/page_reporting.c
@@ -276,7 +276,7 @@  page_reporting_process_zone(struct page_reporting_dev_info *prdev,
 		return err;
 
 	/* Process each free list starting from lowest order/mt */
-	for (order = page_reporting_order; order <= MAX_ORDER; order++) {
+	for (order = page_reporting_order; order < NR_PAGE_ORDERS; order++) {
 		for (mt = 0; mt < MIGRATE_TYPES; mt++) {
 			/* We do not pull pages from the isolate free list */
 			if (is_migrate_isolate(mt))
diff --git a/mm/show_mem.c b/mm/show_mem.c
index ba0808d6917f..8dcfafbd283c 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -352,8 +352,8 @@  static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 
 	for_each_populated_zone(zone) {
 		unsigned int order;
-		unsigned long nr[MAX_ORDER + 1], flags, total = 0;
-		unsigned char types[MAX_ORDER + 1];
+		unsigned long nr[NR_PAGE_ORDERS], flags, total = 0;
+		unsigned char types[NR_PAGE_ORDERS];
 
 		if (zone_idx(zone) > max_zone_idx)
 			continue;
@@ -363,7 +363,7 @@  static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 		printk(KERN_CONT "%s: ", zone->name);
 
 		spin_lock_irqsave(&zone->lock, flags);
-		for (order = 0; order <= MAX_ORDER; order++) {
+		for (order = 0; order < NR_PAGE_ORDERS; order++) {
 			struct free_area *area = &zone->free_area[order];
 			int type;
 
@@ -377,7 +377,7 @@  static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 			}
 		}
 		spin_unlock_irqrestore(&zone->lock, flags);
-		for (order = 0; order <= MAX_ORDER; order++) {
+		for (order = 0; order < NR_PAGE_ORDERS; order++) {
 			printk(KERN_CONT "%lu*%lukB ",
 			       nr[order], K(1UL) << order);
 			if (nr[order])
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 359460deb377..fa7d93e97f7f 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1059,7 +1059,7 @@  static void fill_contig_page_info(struct zone *zone,
 	info->free_blocks_total = 0;
 	info->free_blocks_suitable = 0;
 
-	for (order = 0; order <= MAX_ORDER; order++) {
+	for (order = 0; order < NR_PAGE_ORDERS; order++) {
 		unsigned long blocks;
 
 		/*
@@ -1475,7 +1475,7 @@  static void frag_show_print(struct seq_file *m, pg_data_t *pgdat,
 	int order;
 
 	seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
-	for (order = 0; order <= MAX_ORDER; ++order)
+	for (order = 0; order < NR_PAGE_ORDERS; ++order)
 		/*
 		 * Access to nr_free is lockless as nr_free is used only for
 		 * printing purposes. Use data_race to avoid KCSAN warning.
@@ -1504,7 +1504,7 @@  static void pagetypeinfo_showfree_print(struct seq_file *m,
 					pgdat->node_id,
 					zone->name,
 					migratetype_names[mtype]);
-		for (order = 0; order <= MAX_ORDER; ++order) {
+		for (order = 0; order < NR_PAGE_ORDERS; ++order) {
 			unsigned long freecount = 0;
 			struct free_area *area;
 			struct list_head *curr;
@@ -1544,7 +1544,7 @@  static void pagetypeinfo_showfree(struct seq_file *m, void *arg)
 
 	/* Print header */
 	seq_printf(m, "%-43s ", "Free pages count per migrate type at order");
-	for (order = 0; order <= MAX_ORDER; ++order)
+	for (order = 0; order < NR_PAGE_ORDERS; ++order)
 		seq_printf(m, "%6d ", order);
 	seq_putc(m, '\n');
 
@@ -2180,7 +2180,7 @@  static void unusable_show_print(struct seq_file *m,
 	seq_printf(m, "Node %d, zone %8s ",
 				pgdat->node_id,
 				zone->name);
-	for (order = 0; order <= MAX_ORDER; ++order) {
+	for (order = 0; order < NR_PAGE_ORDERS; ++order) {
 		fill_contig_page_info(zone, order, &info);
 		index = unusable_free_index(order, &info);
 		seq_printf(m, "%d.%03d ", index / 1000, index % 1000);
@@ -2232,7 +2232,7 @@  static void extfrag_show_print(struct seq_file *m,
 	seq_printf(m, "Node %d, zone %8s ",
 				pgdat->node_id,
 				zone->name);
-	for (order = 0; order <= MAX_ORDER; ++order) {
+	for (order = 0; order < NR_PAGE_ORDERS; ++order) {
 		fill_contig_page_info(zone, order, &info);
 		index = __fragmentation_index(order, &info);
 		seq_printf(m, "%2d.%03d ", index / 1000, index % 1000);