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

From: Jonathan Maxwell
Date: Thu Jan 12 2023 - 16:57:41 EST

Hi Andrea,

On Fri, Jan 13, 2023 at 7:41 AM Andrea Mayer <andrea.mayer@xxxxxxxxxxx> wrote:
>
> 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?
>

No, That is for Ipv4, DavidA asked me to include a comparison between Ipv4
and Ipv6. So that is taken for a test running 5 processes that sends 5000000
packets on an ipv4 raw socket. If you scroll down, Ipv6 memory statistics
are under "Ipv6 with patch:".

Regards

Jon

> 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