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

From: Pankaj Gupta <[email-masked]>
Date: Thu, 4 Dec 2014 05:45:01 -0500 (EST)

> 
> 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.

I will make the changes with the next version.
Thanks,
Pankaj
> 
> >  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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