netdev - Re: [net-next rfc 1/3] net: avoid high order memory allocation for queues by using flex array

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Date:	Wed, 19 Jun 2013 21:07:09 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jason Wang <jasowang@...hat.com>, davem@...emloft.net,
	edumazet@...gle.com, hkchu@...gle.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [net-next rfc 1/3] net: avoid high order memory allocation for
 queues by using flex array

On Wed, Jun 19, 2013 at 08:58:31AM -0700, Eric Dumazet wrote:
> On Wed, 2013-06-19 at 18:40 +0300, Michael S. Tsirkin wrote:
> 
> > That's a good trick too - vmalloc memory is a bit slower
> > on x86 since it's not using a huge page, but that's only
> > when we have lots of CPUs/queues...
> > 
> > Short term - how about switching to vmalloc if > 32 queues?
> 
> You do not have to switch "if > 32 queues"
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index fa007db..473cc9e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -130,6 +130,7 @@
>  #include <linux/cpu_rmap.h>
>  #include <linux/static_key.h>
>  #include <linux/hashtable.h>
> +#include <linux/vmalloc.h>
>  
>  #include "net-sysfs.h"
>  
> @@ -5253,6 +5254,14 @@ static void netdev_init_one_queue(struct net_device *dev,
>  #endif
>  }
>  
> +static void netif_free_tx_queues(struct net_device *dev)
> +{
> +	if (is_vmalloc_addr(dev->_tx))
> +		vfree(dev->_tx);
> +	else
> +		kfree(dev->_tx);
> +}
> +
>  static int netif_alloc_netdev_queues(struct net_device *dev)
>  {
>  	unsigned int count = dev->num_tx_queues;
> @@ -5261,9 +5270,11 @@ static int netif_alloc_netdev_queues(struct net_device *dev)
>  	BUG_ON(count < 1);
>  
>  	tx = kcalloc(count, sizeof(struct netdev_queue), GFP_KERNEL);

As we have explicit code to recover, maybe set __GFP_NOWARN?
If we are out of memory, vzalloc will warn too, we don't
need two warnings.

> -	if (!tx)
> -		return -ENOMEM;
> -
> +	if (!tx) {
> +		tx = vzalloc(count * sizeof(struct netdev_queue));
> +		if (!tx)
> +			return -ENOMEM;
> +	}
>  	dev->_tx = tx;
>  
>  	netdev_for_each_tx_queue(dev, netdev_init_one_queue, NULL);
> @@ -5811,7 +5822,7 @@ free_all:
>  
>  free_pcpu:
>  	free_percpu(dev->pcpu_refcnt);
> -	kfree(dev->_tx);
> +	netif_free_tx_queues(dev);
>  #ifdef CONFIG_RPS
>  	kfree(dev->_rx);
>  #endif
> @@ -5836,7 +5847,7 @@ void free_netdev(struct net_device *dev)
>  
>  	release_net(dev_net(dev));
>  
> -	kfree(dev->_tx);
> +	netif_free_tx_queues(dev);
>  #ifdef CONFIG_RPS
>  	kfree(dev->_rx);
>  #endif
> 
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