[RFC PATCH v2 11/12] mm: introduce MIN_MAX_ORDER to replace MAX_ORDER as compile time constant.

[Zi Yan <zi.yan@sent.com>]

From: Zi Yan <ziy@nvidia.com>

For other MAX_ORDER uses (described below), there is no need or too much
hassle to convert certain static array to dynamic ones. Add
MIN_MAX_ORDER to serve as compile time constant in place of MAX_ORDER.

ARM64 hypervisor maintains its own free page list and does not import
any core kernel symbols, so soon-to-be runtime variable MAX_ORDER is not
accessible in ARM64 hypervisor code. Also there is no need to allocating
very large pages.

In SLAB/SLOB/SLUB, 2-D array kmalloc_caches uses MAX_ORDER in its second
dimension. It is too much hassle to allocate memory for kmalloc_caches
before any proper memory allocator is set up.

Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Quentin Perret <qperret@google.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kvmarm@lists.cs.columbia.edu
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 arch/arm64/kvm/hyp/include/nvhe/gfp.h | 2 +-
 arch/arm64/kvm/hyp/nvhe/page_alloc.c  | 2 +-
 include/linux/mmzone.h                | 3 +++
 include/linux/slab.h                  | 8 ++++----
 mm/slab.c                             | 2 +-
 mm/slub.c                             | 6 +++---
 6 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/gfp.h b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
index fe5472a184a3..29b92f68ab69 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[MIN_MAX_ORDER + 1];
 	phys_addr_t range_start;
 	phys_addr_t range_end;
 	unsigned short max_order;
diff --git a/arch/arm64/kvm/hyp/nvhe/page_alloc.c b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
index d40f0b30b534..7ebbac3e2e76 100644
--- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
+++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
@@ -241,7 +241,7 @@ int hyp_pool_init(struct hyp_pool *pool, u64 pfn, unsigned int nr_pages,
 	int i;
 
 	hyp_spin_lock_init(&pool->lock);
-	pool->max_order = min(MAX_ORDER, get_order((nr_pages + 1) << PAGE_SHIFT));
+	pool->max_order = min(MIN_MAX_ORDER, get_order((nr_pages + 1) << PAGE_SHIFT));
 	for (i = 0; i < pool->max_order; i++)
 		INIT_LIST_HEAD(&pool->free_area[i]);
 	pool->range_start = phys;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 60d8cce2aed8..b5774e4c2700 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -26,10 +26,13 @@
 /* Free memory management - zoned buddy allocator.  */
 #ifdef CONFIG_SET_MAX_ORDER
 #define MAX_ORDER CONFIG_SET_MAX_ORDER
+#define MIN_MAX_ORDER CONFIG_SET_MAX_ORDER
 #elif CONFIG_ARCH_FORCE_MAX_ORDER != 0
 #define MAX_ORDER CONFIG_ARCH_FORCE_MAX_ORDER
+#define MIN_MAX_ORDER CONFIG_ARCH_FORCE_MAX_ORDER
 #else
 #define MAX_ORDER 10
+#define MIN_MAX_ORDER MAX_ORDER
 #endif
 
 #define MAX_ORDER_NR_PAGES (1 << MAX_ORDER)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 568b5dfb3bd9..e34b2c9bda09 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -251,8 +251,8 @@ static inline unsigned int arch_slab_minalign(void)
  * to do various tricks to work around compiler limitations in order to
  * ensure proper constant folding.
  */
-#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT) <= 25 ? \
-				(MAX_ORDER + PAGE_SHIFT) : 25)
+#define KMALLOC_SHIFT_HIGH	((MIN_MAX_ORDER + PAGE_SHIFT) <= 25 ? \
+				(MIN_MAX_ORDER + PAGE_SHIFT) : 25)
 #define KMALLOC_SHIFT_MAX	KMALLOC_SHIFT_HIGH
 #ifndef KMALLOC_SHIFT_LOW
 #define KMALLOC_SHIFT_LOW	5
@@ -265,7 +265,7 @@ static inline unsigned int arch_slab_minalign(void)
  * (PAGE_SIZE*2).  Larger requests are passed to the page allocator.
  */
 #define KMALLOC_SHIFT_HIGH	(PAGE_SHIFT + 1)
-#define KMALLOC_SHIFT_MAX	(MAX_ORDER + PAGE_SHIFT)
+#define KMALLOC_SHIFT_MAX	(MIN_MAX_ORDER + PAGE_SHIFT)
 #ifndef KMALLOC_SHIFT_LOW
 #define KMALLOC_SHIFT_LOW	3
 #endif
@@ -278,7 +278,7 @@ static inline unsigned int arch_slab_minalign(void)
  * be allocated from the same page.
  */
 #define KMALLOC_SHIFT_HIGH	PAGE_SHIFT
-#define KMALLOC_SHIFT_MAX	(MAX_ORDER + PAGE_SHIFT)
+#define KMALLOC_SHIFT_MAX	(MIN_MAX_ORDER + PAGE_SHIFT)
 #ifndef KMALLOC_SHIFT_LOW
 #define KMALLOC_SHIFT_LOW	3
 #endif
diff --git a/mm/slab.c b/mm/slab.c
index 530f418a4930..23798c32bb38 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -466,7 +466,7 @@ static int __init slab_max_order_setup(char *str)
 {
 	get_option(&str, &slab_max_order);
 	slab_max_order = slab_max_order < 0 ? 0 :
-				min(slab_max_order, MAX_ORDER);
+				min(slab_max_order, MIN_MAX_ORDER);
 	slab_max_order_set = true;
 
 	return 1;
diff --git a/mm/slub.c b/mm/slub.c
index 5acf5407cbc6..940fe48ea298 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3876,8 +3876,8 @@ static inline int calculate_order(unsigned int size)
 	/*
 	 * Doh this slab cannot be placed using slub_max_order.
 	 */
-	order = calc_slab_order(size, 1, MAX_ORDER, 1);
-	if (order <= MAX_ORDER)
+	order = calc_slab_order(size, 1, MIN_MAX_ORDER, 1);
+	if (order <= MIN_MAX_ORDER)
 		return order;
 	return -ENOSYS;
 }
@@ -4388,7 +4388,7 @@ __setup("slub_min_order=", setup_slub_min_order);
 static int __init setup_slub_max_order(char *str)
 {
 	get_option(&str, (int *)&slub_max_order);
-	slub_max_order = min_t(unsigned int, slub_max_order, MAX_ORDER);
+	slub_max_order = min_t(unsigned int, slub_max_order, MIN_MAX_ORDER);
 
 	return 1;
 }
-- 
2.35.1