staging: ion: optimize struct ion_system_heap

struct ion_system_heap has an array for storing pointers to page pools
and it is allocated separately from the containing structure. There is
no point in allocating those two small objects individually, bothering
slab allocator. Using a variable length array simplifies code lines and
reduces overhead to the slab.
Signed-off-by: Heesub Shin <heesub.shin@samsung.com>
Reviewed-by: Mitchel Humpherys <mitchelh@codeaurora.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion_system_heap.c

@@ -49,7 +49,7 @@ static inline unsigned int order_to_size(int order)
 
 struct ion_system_heap {
 	struct ion_heap heap;
-	struct ion_page_pool **pools;
+	struct ion_page_pool *pools[0];
 };
 
 static struct page *alloc_buffer_page(struct ion_system_heap *heap,
@@ -264,16 +264,15 @@ struct ion_heap *ion_system_heap_create(struct ion_platform_heap *unused)
 	struct ion_system_heap *heap;
 	int i;
 
-	heap = kzalloc(sizeof(struct ion_system_heap), GFP_KERNEL);
+	heap = kzalloc(sizeof(struct ion_system_heap) +
+			sizeof(struct ion_page_pool *) * num_orders,
+			GFP_KERNEL);
 	if (!heap)
 		return ERR_PTR(-ENOMEM);
 	heap->heap.ops = &system_heap_ops;
 	heap->heap.type = ION_HEAP_TYPE_SYSTEM;
 	heap->heap.flags = ION_HEAP_FLAG_DEFER_FREE;
-	heap->pools = kzalloc(sizeof(struct ion_page_pool *) * num_orders,
-			      GFP_KERNEL);
-	if (!heap->pools)
-		goto free_heap;
+
 	for (i = 0; i < num_orders; i++) {
 		struct ion_page_pool *pool;
 		gfp_t gfp_flags = low_order_gfp_flags;
@@ -292,8 +291,6 @@ struct ion_heap *ion_system_heap_create(struct ion_platform_heap *unused)
 destroy_pools:
 	while (i--)
 		ion_page_pool_destroy(heap->pools[i]);
-	kfree(heap->pools);
-free_heap:
 	kfree(heap);
 	return ERR_PTR(-ENOMEM);
 }