[RFC PATCH 14/15] mm: introduce MIN_MAX_ORDER to replace MAX_ORDER as compile time constant.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Quentin Perret <qperret@xxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/arm64/kvm/hyp/include/nvhe/gfp.h | 2 +-
 arch/arm64/kvm/hyp/nvhe/page_alloc.c  | 3 ++-
 include/linux/mmzone.h                | 3 +++
 include/linux/slab.h                  | 8 ++++----
 mm/slab.c                             | 2 +-
 mm/slub.c                             | 7 ++++---
 6 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/gfp.h b/arch/arm64/kvm/hyp/include/nvhe/gfp.h
index fb0f523d1492..c774b4a98336 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];
+	struct list_head free_area[MIN_MAX_ORDER];
 	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 41fc25bdfb34..a1cc1b648de0 100644
--- a/arch/arm64/kvm/hyp/nvhe/page_alloc.c
+++ b/arch/arm64/kvm/hyp/nvhe/page_alloc.c
@@ -226,7 +226,8 @@ 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 << PAGE_SHIFT));
+
+	pool->max_order = min(MIN_MAX_ORDER, get_order(nr_pages << 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 09aafc05aef4..379dada82d4b 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -27,11 +27,14 @@
 #ifndef CONFIG_ARCH_FORCE_MAX_ORDER
 #ifdef CONFIG_SET_MAX_ORDER
 #define MAX_ORDER CONFIG_SET_MAX_ORDER
+#define MIN_MAX_ORDER CONFIG_SET_MAX_ORDER
 #else
 #define MAX_ORDER 11
+#define MIN_MAX_ORDER MAX_ORDER
 #endif /* CONFIG_SET_MAX_ORDER */
 #else
 #define MAX_ORDER CONFIG_ARCH_FORCE_MAX_ORDER
+#define MIN_MAX_ORDER CONFIG_ARCH_FORCE_MAX_ORDER
 #endif /* CONFIG_ARCH_FORCE_MAX_ORDER */
 #define MAX_ORDER_NR_PAGES (1 << (MAX_ORDER - 1))
 
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 2c0d80cca6b8..d8747c158db6 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -244,8 +244,8 @@ static inline void __check_heap_object(const void *ptr, unsigned long n,
  * to do various tricks to work around compiler limitations in order to
  * ensure proper constant folding.
  */
-#define KMALLOC_SHIFT_HIGH	((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
-				(MAX_ORDER + PAGE_SHIFT - 1) : 25)
+#define KMALLOC_SHIFT_HIGH	((MIN_MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
+				(MIN_MAX_ORDER + PAGE_SHIFT - 1) : 25)
 #define KMALLOC_SHIFT_MAX	KMALLOC_SHIFT_HIGH
 #ifndef KMALLOC_SHIFT_LOW
 #define KMALLOC_SHIFT_LOW	5
@@ -258,7 +258,7 @@ static inline void __check_heap_object(const void *ptr, unsigned long n,
  * (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 - 1)
+#define KMALLOC_SHIFT_MAX	(MIN_MAX_ORDER + PAGE_SHIFT - 1)
 #ifndef KMALLOC_SHIFT_LOW
 #define KMALLOC_SHIFT_LOW	3
 #endif
@@ -271,7 +271,7 @@ static inline void __check_heap_object(const void *ptr, unsigned long n,
  * be allocated from the same page.
  */
 #define KMALLOC_SHIFT_HIGH	PAGE_SHIFT
-#define KMALLOC_SHIFT_MAX	(MAX_ORDER + PAGE_SHIFT - 1)
+#define KMALLOC_SHIFT_MAX	(MIN_MAX_ORDER + PAGE_SHIFT - 1)
 #ifndef KMALLOC_SHIFT_LOW
 #define KMALLOC_SHIFT_LOW	3
 #endif
diff --git a/mm/slab.c b/mm/slab.c
index d0f725637663..0041de8ec0e9 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 - 1);
+				min(slab_max_order, MIN_MAX_ORDER - 1);
 	slab_max_order_set = true;
 
 	return 1;
diff --git a/mm/slub.c b/mm/slub.c
index b6c5205252eb..228e4a77c678 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3564,8 +3564,9 @@ static inline int calculate_order(unsigned int size)
 	/*
 	 * Doh this slab cannot be placed using slub_max_order.
 	 */
-	order = slab_order(size, 1, MAX_ORDER, 1);
-	if (order < MAX_ORDER)
+
+	order = slab_order(size, 1, MIN_MAX_ORDER, 1);
+	if (order < MIN_MAX_ORDER)
 		return order;
 	return -ENOSYS;
 }
@@ -4079,7 +4080,7 @@ __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(slub_max_order, (unsigned int)MAX_ORDER - 1);
+	slub_max_order = min(slub_max_order, (unsigned int)MIN_MAX_ORDER - 1);
 
 	return 1;
 }
-- 
2.30.2