Subject: Re: [PATCH] net: factorize rt_do_flush for batch device unregistering

From: Eric Dumazet <[email-masked]>
Date: Mon, 16 Nov 2009 22:32:55 +0100

Octavian Purdila a écrit :
> Tests performed with per device sysctl/sysfs entries disabled:
> 
> $ insmod /lib/modules/dummy.ko numdummies=8000
> $ time rmmod dummy
> 
> Without the patch:    With the patch:
> real    0m 3.65s      real    0m 0.27s
> user    0m 0.00s      user    0m 0.00s
> sys     0m 3.42s      sys     0m 0.24s
> 
> Signed-off-by: Octavian Purdila <[email-masked]>
> ---
>  net/core/dev.c          |   28 ++++++++++++++++++++++++++--
>  net/ipv4/fib_frontend.c |   13 ++++++++-----
>  2 files changed, 34 insertions(+), 7 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 4b24d79..b0a14f0 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4720,7 +4720,8 @@ static void net_set_todo(struct net_device *dev)
>  
>  static void rollback_registered_many(struct list_head *head)
>  {
> -	struct net_device *dev;
> +	struct net_device *dev, *aux, *fdev;
> +	LIST_HEAD(rt_flush_list);
>  
>  	BUG_ON(dev_boot_phase);
>  	ASSERT_RTNL();
> @@ -4778,8 +4779,28 @@ static void rollback_registered_many(struct list_head *head)
>  
>  	synchronize_net();
>  
> -	list_for_each_entry(dev, head, unreg_list)
> +	/* flush route cache by resending one NETDEV_UNREGISTER per namespace */
> +	list_for_each_entry_safe(dev, aux, head, unreg_list) {
> +		int needs_flush = 1;
> +		list_for_each_entry(fdev, &rt_flush_list, unreg_list) {
> +			if (dev_net(dev) == dev_net(fdev)) {
> +				needs_flush = 0;
> +				dev_put(dev);
> +				break;
> +			}
> +		}
> +		if (needs_flush) {
> +			list_del(&dev->unreg_list);
> +			list_add(&dev->unreg_list, &rt_flush_list);

list_move ...

> +		}
> +	}
> +
> +	list_for_each_entry_safe(dev, aux, &rt_flush_list, unreg_list) {
> +		list_del_init(&dev->unreg_list);
> +		call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
> +		list_add(&dev->unreg_list, head);
>  		dev_put(dev);
> +	}
>  }
>  
>  static void rollback_registered(struct net_device *dev)
> @@ -5374,6 +5395,9 @@ EXPORT_SYMBOL(unregister_netdevice_queue);
>   *	unregister_netdevice_many - unregister many devices
>   *	@head: list of devices
>   *
> + *	WARNING: This function modifies the list. It may change the order of the
> + *	elements in the list. However, you can assume it does not add or delete
> + *	elements to/from the list.

Sorry I dont understand this comment

>   */
>  void unregister_netdevice_many(struct list_head *head)
>  {
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 816e218..1972760 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -895,11 +895,11 @@ static void nl_fib_lookup_exit(struct net *net)
>  	net->ipv4.fibnl = NULL;
>  }
>  
> -static void fib_disable_ip(struct net_device *dev, int force)
> +static void fib_disable_ip(struct net_device *dev, int force, int delay)
>  {
>  	if (fib_sync_down_dev(dev, force))
>  		fib_flush(dev_net(dev));
> -	rt_cache_flush(dev_net(dev), 0);
> +	rt_cache_flush(dev_net(dev), delay);
>  	arp_ifdown(dev);
>  }
>  
> @@ -922,7 +922,7 @@ static int fib_inetaddr_event(struct notifier_block *this, unsigned long event,
>  			/* Last address was deleted from this interface.
>  			   Disable IP.
>  			 */
> -			fib_disable_ip(dev, 1);
> +			fib_disable_ip(dev, 1, 0);
>  		} else {
>  			rt_cache_flush(dev_net(dev), -1);
>  		}
> @@ -937,7 +937,10 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
>  	struct in_device *in_dev = __in_dev_get_rtnl(dev);
>  
>  	if (event == NETDEV_UNREGISTER) {
> -		fib_disable_ip(dev, 2);
> +		/* if this event is part of a batch then don't flush the cache
> +		 * now; we will receive another event at the end of the batch */
> +		int rt_flush = list_empty(&dev->unreg_list) ? 0 : -1;

hmm... a bit ugly...

> +		fib_disable_ip(dev, 2, rt_flush);
>  		return NOTIFY_DONE;
>  	}
>  
> @@ -955,7 +958,7 @@ static int fib_netdev_event(struct notifier_block *this, unsigned long event, vo
>  		rt_cache_flush(dev_net(dev), -1);
>  		break;
>  	case NETDEV_DOWN:
> -		fib_disable_ip(dev, 0);
> +		fib_disable_ip(dev, 0, 0);
>  		break;
>  	case NETDEV_CHANGEMTU:
>  	case NETDEV_CHANGE:

Are you sure you want to overload NETDEV_UNREGISTER ?

Maybe it would be cleaner to add a new value, NETDEV_UNREGISTER_PERNET or something 
for the final loop...