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inetpeer: get rid of ip_id_count

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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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2014-06-02 05:26:03 -07:00
committed by David S. Miller
parent e067ee336a
commit 73f156a6e8
17 changed files with 66 additions and 156 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
include/net/inetpeer.h
View File

@@ -41,14 +41,13 @@ struct inet_peer {
struct rcu_head gc_rcu;
};
/*
* Once inet_peer is queued for deletion (refcnt == -1), following fields
* are not available: rid, ip_id_count
* Once inet_peer is queued for deletion (refcnt == -1), following field
* is not available: rid
* We can share memory with rcu_head to help keep inet_peer small.
*/
union {
struct {
atomic_t rid; /* Frag reception counter */
atomic_t ip_id_count; /* IP ID for the next packet */
};
struct rcu_head rcu;
struct inet_peer *gc_next;
@@ -165,7 +164,7 @@ bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout);
void inetpeer_invalidate_tree(struct inet_peer_base *);
/*
* temporary check to make sure we dont access rid, ip_id_count, tcp_ts,
* temporary check to make sure we dont access rid, tcp_ts,
* tcp_ts_stamp if no refcount is taken on inet_peer
*/
static inline void inet_peer_refcheck(const struct inet_peer *p)
@@ -173,20 +172,4 @@ static inline void inet_peer_refcheck(const struct inet_peer *p)
WARN_ON_ONCE(atomic_read(&p->refcnt) <= 0);
}
/* can be called with or without local BH being disabled */
static inline int inet_getid(struct inet_peer *p, int more)
{
int old, new;
more++;
inet_peer_refcheck(p);
do {
old = atomic_read(&p->ip_id_count);
new = old + more;
if (!new)
new = 1;
} while (atomic_cmpxchg(&p->ip_id_count, old, new) != old);
return new;
}
#endif /* _NET_INETPEER_H */