>Using order 4 pages would be helpful for IOMMUs mapping, but trying to get order 4 pages could spend quite much time in the page allocation.
>From the perspective of responsiveness, the deterministic memory allocation speed, I think, is quite important.
>
>The order 4 allocation with __GFP_RECLAIM may spend much time in reclaim and compation logic. __GFP_NORETRY also may affect. These cause unpredictable delay.
>
>To get reasonable allocation speed from dma-buf system heap, use HIGH_ORDER_GFP for order 4 to avoid reclaim. And let me remove meaningless __GFP_COMP for order 0.
>
>According to my tests, order 4 with MID_ORDER_GFP could get more number of order 4 pages but the elapsed times could be very slow.
>
> time order 8 order 4 order 0
> 584 usec 0 160 0
> 28,428 usec 0 160 0
> 100,701 usec 0 160 0
> 76,645 usec 0 160 0
> 25,522 usec 0 160 0
> 38,798 usec 0 160 0
> 89,012 usec 0 160 0
> 23,015 usec 0 160 0
> 73,360 usec 0 160 0
> 76,953 usec 0 160 0
> 31,492 usec 0 160 0
> 75,889 usec 0 160 0
> 84,551 usec 0 160 0
> 84,352 usec 0 160 0
> 57,103 usec 0 160 0
> 93,452 usec 0 160 0
>
>If HIGH_ORDER_GFP is used for order 4, the number of order 4 could be decreased but the elapsed time results were quite stable and fast enough.
>
> time order 8 order 4 order 0
> 1,356 usec 0 155 80
> 1,901 usec 0 11 2384
> 1,912 usec 0 0 2560
> 1,911 usec 0 0 2560
> 1,884 usec 0 0 2560
> 1,577 usec 0 0 2560
> 1,366 usec 0 0 2560
> 1,711 usec 0 0 2560
> 1,635 usec 0 28 2112
> 544 usec 10 0 0
> 633 usec 2 128 0
> 848 usec 0 160 0
> 729 usec 0 160 0
> 1,000 usec 0 160 0
> 1,358 usec 0 160 0
> 2,638 usec 0 31 2064
>
>Signed-off-by: Jaewon Kim <jaewon31.kim@xxxxxxxxxxx>
>---
> drivers/dma-buf/heaps/system_heap.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
>index e8bd10e60998..920db302a273 100644
>--- a/drivers/dma-buf/heaps/system_heap.c
>+++ b/drivers/dma-buf/heaps/system_heap.c
>@@ -41,12 +41,11 @@ struct dma_heap_attachment {
> bool mapped;
> };
>
>-#define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO | __GFP_COMP) -#define MID_ORDER_GFP (LOW_ORDER_GFP | __GFP_NOWARN)
>+#define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO)
> #define HIGH_ORDER_GFP (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \
> | __GFP_NORETRY) & ~__GFP_RECLAIM) \
> | __GFP_COMP)
>-static gfp_t order_flags[] = {HIGH_ORDER_GFP, MID_ORDER_GFP, LOW_ORDER_GFP};
>+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
>--
>2.17.1
>
>
added John Stultz <jstultz@xxxxxxxxxx>
