linux-kernel - [PATCH] dma-buf: system_heap: avoid reclaim for order 4

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Date:   Tue, 17 Jan 2023 17:25:08 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     john.stultz@...aro.org, sumit.semwal@...aro.org,
        daniel.vetter@...ll.ch, akpm@...ux-foundation.org,
        hannes@...xchg.org, mhocko@...nel.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        jaewon31.kim@...il.com, Jaewon Kim <jaewon31.kim@...sung.com>
Subject: [PATCH] dma-buf: system_heap: avoid reclaim for order 4

Using order 4 pages would be helpful for many IOMMUs, but it could spend
quite much time in page allocation perspective.

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.

Signed-off-by: Jaewon Kim <jaewon31.kim@...sung.com>
---
 drivers/dma-buf/heaps/system_heap.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index e8bd10e60998..5a405e99ef1e 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -42,11 +42,10 @@ struct dma_heap_attachment {
 };
 
 #define LOW_ORDER_GFP (GFP_HIGHUSER | __GFP_ZERO | __GFP_COMP)
-#define MID_ORDER_GFP (LOW_ORDER_GFP | __GFP_NOWARN)
 #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