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inetpeer: get rid of ip_id_count

Browse source 
Ideally, we would need to generate IP ID using a per destination IP
generator.

linux kernels used inet_peer cache for this purpose, but this had a huge
cost on servers disabling MTU discovery.

1) each inet_peer struct consumes 192 bytes

2) inetpeer cache uses a binary tree of inet_peer structs,
   with a nominal size of ~66000 elements under load.

3) lookups in this tree are hitting a lot of cache lines, as tree depth
   is about 20.

4) If server deals with many tcp flows, we have a high probability of
   not finding the inet_peer, allocating a fresh one, inserting it in
   the tree with same initial ip_id_count, (cf secure_ip_id())

5) We garbage collect inet_peer aggressively.

IP ID generation do not have to be 'perfect'

Goal is trying to avoid duplicates in a short period of time,
so that reassembly units have a chance to complete reassembly of
fragments belonging to one message before receiving other fragments
with a recycled ID.

We simply use an array of generators, and a Jenkin hash using the dst IP
as a key.

ipv6_select_ident() is put back into net/ipv6/ip6_output.c where it
belongs (it is only used from this file)

secure_ip_id() and secure_ipv6_id() no longer are needed.

Rename ip_select_ident_more() to ip_select_ident_segs() to avoid
unnecessary decrement/increment of the number of segments.

Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2014-06-02 05:26:03 -07:00 • committed by David S. Miller
commit 73f156a6e8
17 changed files with 65 additions and 155 deletions
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12
net/ipv6/ip6_output.c
View file

@ -537,6 +537,18 @@ static void ip6_copy_metadata(struct sk_buff *to, struct sk_buff *from)
skb_copy_secmark(to, from);
}
static void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
{
static u32 ip6_idents_hashrnd __read_mostly;
u32 hash, id;
net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd));
hash = __ipv6_addr_jhash(&rt->rt6i_dst.addr, ip6_idents_hashrnd);
id = ip_idents_reserve(hash, 1);
fhdr->identification = htonl(id);
}
int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
{
struct sk_buff *frag;

30
net/ipv6/output_core.c
View file

@ -8,36 +8,6 @@
#include <net/addrconf.h>
#include <net/secure_seq.h>
void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
{
static atomic_t ipv6_fragmentation_id;
struct in6_addr addr;
int old, new;
#if IS_ENABLED(CONFIG_IPV6)
struct inet_peer *peer;
struct net *net;
net = dev_net(rt->dst.dev);
peer = inet_getpeer_v6(net->ipv6.peers, &rt->rt6i_dst.addr, 1);
if (peer) {
fhdr->identification = htonl(inet_getid(peer, 0));
inet_putpeer(peer);
return;
}
#endif
do {
old = atomic_read(&ipv6_fragmentation_id);
new = old + 1;
if (!new)
new = 1;
} while (atomic_cmpxchg(&ipv6_fragmentation_id, old, new) != old);
addr = rt->rt6i_dst.addr;
addr.s6_addr32[0] ^= (__force __be32)new;
fhdr->identification = htonl(secure_ipv6_id(addr.s6_addr32));
}
EXPORT_SYMBOL(ipv6_select_ident);
int ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr)
{