[PATCH v3] dma-buf: system_heap: Set allocation orders for larger page sizes

[Juan Yescas]

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 at google.com>
Acked-by: John Stultz <jstultz at google.com>
Reviewed-by: T.J. Mercier <tjmercier at 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.

Changes in v3:
  - Remove defines for the orders as per Christian.
  - Update the order array for 64k page sizes as per TJ

 drivers/dma-buf/heaps/system_heap.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 26d5dc89ea16..8c10c0f2b473 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -18,6 +18,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/scatterlist.h>
+#include <linux/sizes.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 
@@ -44,14 +45,28 @@ struct dma_heap_attachment {
 #define HIGH_ORDER_GFP  (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \
 				| __GFP_NORETRY) & ~__GFP_RECLAIM) \
 				| __GFP_COMP)
-static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
 /*
  * The selection of the orders used for allocation (1MB, 64K, 4K) is designed
  * 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.
+ */
+#if (PAGE_SIZE == SZ_64K)
+static gfp_t order_flags[] = {HIGH_ORDER_GFP, LOW_ORDER_GFP};
+/* 1MiB allocs are calculated with (2 ^ (20 - PAGE_SHIFT)) * PAGE_SIZE = 1MiB */
+static const unsigned int orders[] = {20 - PAGE_SHIFT, 0};
+#else
+static gfp_t order_flags[] = {HIGH_ORDER_GFP, HIGH_ORDER_GFP, LOW_ORDER_GFP};
+/*
+ * 1MiB allocs are calculated with (2 ^ (20 - PAGE_SHIFT)) * PAGE_SIZE = 1MiB
+ * 64KiB allocs are calculated with (2 ^ (16 - PAGE_SHIFT)) * PAGE_SIZE = 64KiB
  */
-static const unsigned int orders[] = {8, 4, 0};
+static const unsigned int orders[] = {20 - PAGE_SHIFT, 16 - PAGE_SHIFT, 0};
+#endif
+
 #define NUM_ORDERS ARRAY_SIZE(orders)
 
 static struct sg_table *dup_sg_table(struct sg_table *table)
@@ -318,7 +333,7 @@ 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;
-- 
2.49.0.805.g082f7c87e0-goog