dma-buf: system_heap: avoid reclaim for order 4

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

Link: https://lkml.kernel.org/r/20230303050332.10138-1-jaewon31.kim@samsung.comSigned-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
Reviewed-by: John Stultz <jstultz@google.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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