netdev - Re: [PATCH] mlx4_en: don't wait for high order page allocation

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Date:	Fri, 12 Jun 2015 10:05:42 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Shaohua Li <shli@...com>, netdev@...r.kernel.org
CC:	davem@...emloft.net, Kernel-team@...com,
	Amir Vadai <amirv@...lanox.com>,
	Ido Shamay <idos@...lanox.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] mlx4_en: don't wait for high order page allocation

On 06/12/2015 09:50 AM, Shaohua Li wrote:
> High order page allocation can cause direct memory compaction and harm
> performance. The patch makes the high order page allocation don't wait,
> so not trigger direct memory compaction with memory pressure. More
> details can be found in a similar patch for net core:
> http://marc.info/?l=linux-mm&m=143406665720428&w=2
>
> Cc: Amir Vadai <amirv@...lanox.com>
> Cc: Ido Shamay <idos@...lanox.com>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Shaohua Li <shli@...com>
> ---
>   drivers/net/ethernet/mellanox/mlx4/en_rx.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 2a77a6b..9bc4143 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -60,8 +60,11 @@ static int mlx4_alloc_pages(struct mlx4_en_priv *priv,
>   	for (order = MLX4_EN_ALLOC_PREFER_ORDER; ;) {
>   		gfp_t gfp = _gfp;
>   
> -		if (order)
> +		if (order) {
> +			if ((PAGE_SIZE << (order - 1)) >= frag_info->frag_size)
> +				gfp &= ~__GFP_WAIT;
>   			gfp |= __GFP_COMP | __GFP_NOWARN;
> +		}
>   		page = alloc_pages(gfp, order);
>   		if (likely(page))
>   			break;

Is this even really necessary?  I would thing the fact that the refill 
is done using GFP_ATOMIC would be enough to cover the frequently used 
cases.  I wouldn't think the initial allocation when the interface is 
brought up would be something that is a big enough deal to justify being 
fixed in this case.

- Alex
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