[PATCH v2] dma-buf: system_heap: Set allocation orders for larger page sizes

[Juan Yescas <jyescas@google.com>]

This change sets the allocation orders for the different page sizes
(4k, 16k, 64k) based on PAGE_SHIFT. Before this change, the orders
for large page sizes were calculated incorrectly, this caused system
heap to allocate from 2% to 4% more memory on 16KiB page size kernels.

This change was tested on 4k/16k page size kernels.

Signed-off-by: Juan Yescas <jyescas@google.com>
Acked-by: John Stultz <jstultz@google.com>
Reviewed-by: T.J. Mercier <tjmercier@google.com>
---

Changes in v2:
  - Add John's Acked-by tag.
  - Add TJ's Reviewed-by tag
  - Use dma-buf: system_heap: in the subject since this is specific to the
    system heap, as per TJ.
  - Remove extra space in if statement.


 drivers/dma-buf/heaps/system_heap.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 26d5dc89ea16..ffc8f488eca6 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -50,8 +50,15 @@ static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
  * to match with the sizes often found in IOMMUs. Using order 4 pages instead
  * of order 0 pages can significantly improve the performance of many IOMMUs
  * by reducing TLB pressure and time spent updating page tables.
+ *
+ * Note: When the order is 0, the minimum allocation is PAGE_SIZE. The possible
+ * page sizes for ARM devices could be 4K, 16K and 64K.
  */
-static const unsigned int orders[] = {8, 4, 0};
+#define ORDER_1M (20 - PAGE_SHIFT)
+#define ORDER_64K (16 - PAGE_SHIFT)
+#define ORDER_FOR_PAGE_SIZE (0)
+static const unsigned int orders[] = {ORDER_1M, ORDER_64K, ORDER_FOR_PAGE_SIZE};
+
 #define NUM_ORDERS ARRAY_SIZE(orders)
 
 static struct sg_table *dup_sg_table(struct sg_table *table)
@@ -318,7 +325,7 @@ static struct page *alloc_largest_available(unsigned long size,
 	int i;
 
 	for (i = 0; i < NUM_ORDERS; i++) {
-		if (size <  (PAGE_SIZE << orders[i]))
+		if (size < (PAGE_SIZE << orders[i]))
 			continue;
 		if (max_order < orders[i])
 			continue;
-- 
2.49.0.604.gff1f9ca942-goog