[PATCH v2] driver : staging : ion: optimization for decreasing memory fragmentaion

[Zhaoyang Huang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

Two action for this patch:
1. set a batch size for system heap's shrinker, which can have it buffer
reasonable page blocks in pool for future allocation.
2. reverse the order sequence when free page blocks, the purpose is also
to have system heap keep as more big blocks as it can.

By testing on an android system with 2G RAM, the changes with setting
batch = 48MB can help reduce the fragmentation obviously and improve
big block allocation speed for 15%.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 drivers/staging/android/ion/ion_heap.c        | 16 +++++++++++++++-
 drivers/staging/android/ion/ion_system_heap.c |  2 +-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/android/ion/ion_heap.c b/drivers/staging/android/ion/ion_heap.c
index 31db510..0c8d696 100644
--- a/drivers/staging/android/ion/ion_heap.c
+++ b/drivers/staging/android/ion/ion_heap.c
@@ -16,6 +16,8 @@
 #include <linux/vmalloc.h>
 #include "ion.h"
 
+static unsigned long ion_heap_batch;
+
 void *ion_heap_map_kernel(struct ion_heap *heap,
 			  struct ion_buffer *buffer)
 {
@@ -303,7 +305,19 @@ int ion_heap_init_shrinker(struct ion_heap *heap)
 	heap->shrinker.count_objects = ion_heap_shrink_count;
 	heap->shrinker.scan_objects = ion_heap_shrink_scan;
 	heap->shrinker.seeks = DEFAULT_SEEKS;
-	heap->shrinker.batch = 0;
+	heap->shrinker.batch = ion_heap_batch;
 
 	return register_shrinker(&heap->shrinker);
 }
+
+/*
+ * configuring ion_heap_batch as 3 times of the pool's peak value can help
+ * improving allocation speed
+ */
+static int __init ion_system_heap_batch_init(char *arg)
+{
+	ion_heap_batch = memparse(arg, NULL);
+
+	return 0;
+}
+early_param("ion_batch", ion_system_heap_batch_init);
diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
index 701eb9f..d249f8d 100644
--- a/drivers/staging/android/ion/ion_system_heap.c
+++ b/drivers/staging/android/ion/ion_system_heap.c
@@ -182,7 +182,7 @@ static int ion_system_heap_shrink(struct ion_heap *heap, gfp_t gfp_mask,
 	if (!nr_to_scan)
 		only_scan = 1;
 
-	for (i = 0; i < NUM_ORDERS; i++) {
+	for (i = NUM_ORDERS - 1; i >= 0; i--) {
 		pool = sys_heap->pools[i];
 
 		if (only_scan) {
-- 
1.9.1