netdev - Re: [PATCH net-next] mlx4: support __GFP

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Date:   Wed, 18 Jan 2017 12:31:18 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH net-next] mlx4: support __GFP_MEMALLOC for rx

On 18.01.2017 07:14, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Commit 04aeb56a1732 ("net/mlx4_en: allocate non 0-order pages for RX
> ring with __GFP_NOMEMALLOC") added code that appears to be not needed at
> that time, since mlx4 never used __GFP_MEMALLOC allocations anyway.
>
> As using memory reserves is a must in some situations (swap over NFS or
> iSCSI), this patch adds this flag.

AFAIK __GFP_MEMALLOC is used for TX, not for RX: for allocations which are required by memory reclaimer to free some pages.

Allocation RX buffers with __GFP_MEMALLOC is a straight way to depleting all reserves by flood from network.

>
> Note that this driver does not reuse pages (yet) so we do not have to
> add anything else.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Cc: Tariq Toukan <tariqt@...lanox.com>
> ---
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index eac527e25ec902c2a586e9952272b9e8e599e2c8..e362f99334d03c0df4d88320977670015870dd9c 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -706,7 +706,8 @@ static bool mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
>  	do {
>  		if (mlx4_en_prepare_rx_desc(priv, ring,
>  					    ring->prod & ring->size_mask,
> -					    GFP_ATOMIC | __GFP_COLD))
> +					    GFP_ATOMIC | __GFP_COLD |
> +					    __GFP_MEMALLOC))
>  			break;
>  		ring->prod++;
>  	} while (--missing);
>
>


-- 
Konstantin