Subject: Re: [PATCH v3 net-next 1/2] net: allow large number of rx queues

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 3 Dec 2014 11:42:24 +0200

On Wed, Dec 03, 2014 at 12:49:36PM +0530, Pankaj Gupta wrote:
> netif_alloc_rx_queues() uses kcalloc() to allocate memory
> for "struct netdev_queue *_rx" array.
> If we are doing large rx queue allocation kcalloc() might
> fail, so this patch does a fallback to vzalloc().
> Similar implementation is done for tx queue allocation in
> netif_alloc_netdev_queues().
> 
> We avoid failure of high order memory allocation
> with the help of vzalloc(), this allows us to do large
> rx and tx queue allocation which in turn helps us to
> increase the number of queues in tun.
> 
> As vmalloc() adds overhead on a critical network path,
> __GFP_REPEAT flag is used with kzalloc() to do this fallback
> only when really needed.
> 
> Signed-off-by: Pankaj Gupta <[email-masked]>
> Reviewed-by: Michael S. Tsirkin <[email-masked]>
> Reviewed-by: David Gibson <[email-masked]>
> ---
>  net/core/dev.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index e916ba8..abe9560 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6059,17 +6059,25 @@ void netif_stacked_transfer_operstate(const struct net_device *rootdev,
>  EXPORT_SYMBOL(netif_stacked_transfer_operstate);
>  
>  #ifdef CONFIG_SYSFS
> +static void netif_free_rx_queues(struct net_device *dev)
> +{
> +	kvfree(dev->_rx);
> +}
> +

I would just open-code this.

>  static int netif_alloc_rx_queues(struct net_device *dev)
>  {
>  	unsigned int i, count = dev->num_rx_queues;
>  	struct netdev_rx_queue *rx;
> +	size_t sz = count * sizeof(*rx);
>  
>  	BUG_ON(count < 1);
>  
> -	rx = kcalloc(count, sizeof(struct netdev_rx_queue), GFP_KERNEL);
> -	if (!rx)
> -		return -ENOMEM;
> -
> +	rx = kzalloc(sz, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> +	if (!rx) {
> +		rx = vzalloc(sz);
> +		if (!rx)
> +			return -ENOMEM;
> +	}
>  	dev->_rx = rx;
>  
>  	for (i = 0; i < count; i++)
> @@ -6698,9 +6706,8 @@ void free_netdev(struct net_device *dev)
>  
>  	netif_free_tx_queues(dev);
>  #ifdef CONFIG_SYSFS
> -	kfree(dev->_rx);
> +	netif_free_rx_queues(dev);
>  #endif
> -

and I think it's nicer with the empty line.

>  	kfree(rcu_dereference_protected(dev->ingress_queue, 1));
>  
>  	/* Flush device addresses */
> -- 
> 1.8.3.1
> 
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