Re: [net-next v2] ipv6: remove max_size check inline with ipv4

[Andrea Mayer]

Hi Jon,

On Thu, 12 Jan 2023 12:25:32 +1100
Jon Maxwell <jmaxwell37@xxxxxxxxx> wrote:

> v2: Correct syntax error in net/ipv6/route.c
> 
> In ip6_dst_gc() replace: 
> 
> if (entries > gc_thresh)
> 
> With:
> 
> if (entries > ops->gc_thresh)
> 
> Sending Ipv6 packets in a loop via a raw socket triggers an issue where a 
> route is cloned by ip6_rt_cache_alloc() for each packet sent. This quickly 
> consumes the Ipv6 max_size threshold which defaults to 4096 resulting in 
> these warnings:
> 
> [1]   99.187805] dst_alloc: 7728 callbacks suppressed
> [2] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
> .
> .
> [300] Route cache is full: consider increasing sysctl net.ipv6.route.max_size.
> 
> When this happens the packet is dropped and sendto() gets a network is 
> unreachable error:
> 
> # ./a.out -s 
> 
> remaining pkt 200557 errno 101
> remaining pkt 196462 errno 101
> .
> .
> remaining pkt 126821 errno 101
> 
> Implement David Aherns suggestion to remove max_size check seeing that Ipv6 
> has a GC to manage memory usage. Ipv4 already does not check max_size.
> 
> Here are some memory comparisons for Ipv4 vs Ipv6 with the patch:
> 
> Test by running 5 instances of a program that sends UDP packets to a raw 
> socket 5000000 times. Compare Ipv4 and Ipv6 performance with a similar 
> program.
> 
> Ipv4: 
> 

is it supposed to be Ipv6, right?

Ciao,
Andrea

> Before test:
> 
> # grep -e Slab -e Free /proc/meminfo
> MemFree:        29427108 kB
> Slab:             237612 kB
> 
> # grep dst_cache /proc/slabinfo
> ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
> xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
> ip_dst_cache        2881   3990    192   42    2 : tunables    0    0    0 
> 
> During test:
> 
> # grep -e Slab -e Free /proc/meminfo
> MemFree:        29417608 kB
> Slab:             247712 kB
> 
> # grep dst_cache /proc/slabinfo
> ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
> xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
> ip_dst_cache       44394  44394    192   42    2 : tunables    0    0    0 
> 
> After test:
> 
> # grep -e Slab -e Free /proc/meminfo
> MemFree:        29422308 kB
> Slab:             238104 kB
> 
> # grep dst_cache /proc/slabinfo
> ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
> xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
> ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0 
> 
> Ipv6 with patch:
> 
> Errno 101 errors are not observed anymore with the patch.
> 
> Before test:
> 
> # grep -e Slab -e Free /proc/meminfo
> MemFree:        29422308 kB
> Slab:             238104 kB
> 
> # grep dst_cache /proc/slabinfo
> ip6_dst_cache       1912   2528    256   32    2 : tunables    0    0    0 
> xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0 
> ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0 
> 
> During Test:
> 
> # grep -e Slab -e Free /proc/meminfo
> MemFree:        29431516 kB
> Slab:             240940 kB
> 
> # grep dst_cache /proc/slabinfo
> ip6_dst_cache      11980  12064    256   32    2 : tunables    0    0    0
> xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0
> ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0
> 
> After Test:
> 
> # grep -e Slab -e Free /proc/meminfo
> MemFree:        29441816 kB
> Slab:             238132 kB
> 
> # grep dst_cache /proc/slabinfo
> ip6_dst_cache       1902   2432    256   32    2 : tunables    0    0    0
> xfrm_dst_cache         0      0    320   25    2 : tunables    0    0    0
> ip_dst_cache        3048   4116    192   42    2 : tunables    0    0    0
> 
> Tested-by: Andrea Mayer <andrea.mayer@xxxxxxxxxxx>
> Signed-off-by: Jon Maxwell <jmaxwell37@xxxxxxxxx>
> ---
>  include/net/dst_ops.h |  2 +-
>  net/core/dst.c        |  8 ++------
>  net/ipv6/route.c      | 13 +++++--------
>  3 files changed, 8 insertions(+), 15 deletions(-)
> 
> diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
> index 88ff7bb2bb9b..632086b2f644 100644
> --- a/include/net/dst_ops.h
> +++ b/include/net/dst_ops.h
> @@ -16,7 +16,7 @@ struct dst_ops {
>  	unsigned short		family;
>  	unsigned int		gc_thresh;
>  
> -	int			(*gc)(struct dst_ops *ops);
> +	void			(*gc)(struct dst_ops *ops);
>  	struct dst_entry *	(*check)(struct dst_entry *, __u32 cookie);
>  	unsigned int		(*default_advmss)(const struct dst_entry *);
>  	unsigned int		(*mtu)(const struct dst_entry *);
> diff --git a/net/core/dst.c b/net/core/dst.c
> index 6d2dd03dafa8..31c08a3386d3 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -82,12 +82,8 @@ void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
>  
>  	if (ops->gc &&
>  	    !(flags & DST_NOCOUNT) &&
> -	    dst_entries_get_fast(ops) > ops->gc_thresh) {
> -		if (ops->gc(ops)) {
> -			pr_notice_ratelimited("Route cache is full: consider increasing sysctl net.ipv6.route.max_size.\n");
> -			return NULL;
> -		}
> -	}
> +	    dst_entries_get_fast(ops) > ops->gc_thresh)
> +		ops->gc(ops);
>  
>  	dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
>  	if (!dst)
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index e74e0361fd92..b643dda68d31 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -91,7 +91,7 @@ static struct dst_entry *ip6_negative_advice(struct dst_entry *);
>  static void		ip6_dst_destroy(struct dst_entry *);
>  static void		ip6_dst_ifdown(struct dst_entry *,
>  				       struct net_device *dev, int how);
> -static int		 ip6_dst_gc(struct dst_ops *ops);
> +static void		 ip6_dst_gc(struct dst_ops *ops);
>  
>  static int		ip6_pkt_discard(struct sk_buff *skb);
>  static int		ip6_pkt_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb);
> @@ -3284,11 +3284,10 @@ struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
>  	return dst;
>  }
>  
> -static int ip6_dst_gc(struct dst_ops *ops)
> +static void ip6_dst_gc(struct dst_ops *ops)
>  {
>  	struct net *net = container_of(ops, struct net, ipv6.ip6_dst_ops);
>  	int rt_min_interval = net->ipv6.sysctl.ip6_rt_gc_min_interval;
> -	int rt_max_size = net->ipv6.sysctl.ip6_rt_max_size;
>  	int rt_elasticity = net->ipv6.sysctl.ip6_rt_gc_elasticity;
>  	int rt_gc_timeout = net->ipv6.sysctl.ip6_rt_gc_timeout;
>  	unsigned long rt_last_gc = net->ipv6.ip6_rt_last_gc;
> @@ -3296,11 +3295,10 @@ static int ip6_dst_gc(struct dst_ops *ops)
>  	int entries;
>  
>  	entries = dst_entries_get_fast(ops);
> -	if (entries > rt_max_size)
> +	if (entries > ops->gc_thresh)
>  		entries = dst_entries_get_slow(ops);
>  
> -	if (time_after(rt_last_gc + rt_min_interval, jiffies) &&
> -	    entries <= rt_max_size)
> +	if (time_after(rt_last_gc + rt_min_interval, jiffies))
>  		goto out;
>  
>  	fib6_run_gc(atomic_inc_return(&net->ipv6.ip6_rt_gc_expire), net, true);
> @@ -3310,7 +3308,6 @@ static int ip6_dst_gc(struct dst_ops *ops)
>  out:
>  	val = atomic_read(&net->ipv6.ip6_rt_gc_expire);
>  	atomic_set(&net->ipv6.ip6_rt_gc_expire, val - (val >> rt_elasticity));
> -	return entries > rt_max_size;
>  }
>  
>  static int ip6_nh_lookup_table(struct net *net, struct fib6_config *cfg,
> @@ -6512,7 +6509,7 @@ static int __net_init ip6_route_net_init(struct net *net)
>  #endif
>  
>  	net->ipv6.sysctl.flush_delay = 0;
> -	net->ipv6.sysctl.ip6_rt_max_size = 4096;
> +	net->ipv6.sysctl.ip6_rt_max_size = INT_MAX;
>  	net->ipv6.sysctl.ip6_rt_gc_min_interval = HZ / 2;
>  	net->ipv6.sysctl.ip6_rt_gc_timeout = 60*HZ;
>  	net->ipv6.sysctl.ip6_rt_gc_interval = 30*HZ;
> -- 
> 2.31.1