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

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Date:   Tue, 17 Jan 2023 17:31:03 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     Jaewon Kim <jaewon31.kim@...sung.com>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "jstultz@...gle.com" <jstultz@...gle.com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jaewon31.kim@...il.com" <jaewon31.kim@...il.com>
Subject: Re: [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

added John Stultz <jstultz@...gle.com>