tcp/dccp: remove twchain

TCP listener refactoring, part 3 :

Our goal is to hash SYN_RECV sockets into main ehash for fast lookup,
and parallel SYN processing.

Current inet_ehash_bucket contains two chains, one for ESTABLISH (and
friend states) sockets, another for TIME_WAIT sockets only.

As the hash table is sized to get at most one socket per bucket, it
makes little sense to have separate twchain, as it makes the lookup
slightly more complicated, and doubles hash table memory usage.

If we make sure all socket types have the lookup keys at the same
offsets, we can use a generic and faster lookup. It turns out TIME_WAIT
and ESTABLISHED sockets already have common lookup fields for IPv4.

[ INET_TW_MATCH() is no longer needed ]

I'll provide a follow-up to factorize IPv6 lookup as well, to remove
INET6_TW_MATCH()

This way, SYN_RECV pseudo sockets will be supported the same.

A new sock_gen_put() helper is added, doing either a sock_put() or
inet_twsk_put() [ and will support SYN_RECV later ].

Note this helper should only be called in real slow path, when rcu
lookup found a socket that was moved to another identity (freed/reused
immediately), but could eventually be used in other contexts, like
sock_edemux()

Before patch :

dmesg | grep "TCP established"

TCP established hash table entries: 524288 (order: 11, 8388608 bytes)

After patch :

TCP established hash table entries: 524288 (order: 10, 4194304 bytes)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 7 deletions

diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index 10d6838..1bdb477 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -37,12 +37,11 @@
 #include <asm/byteorder.h>
 
 /* This is for all connections with a full identity, no wildcards.
- * One chain is dedicated to TIME_WAIT sockets.
- * I'll experiment with dynamic table growth later.
+ * The 'e' prefix stands for Establish, but we really put all sockets
+ * but LISTEN ones.
  */
 struct inet_ehash_bucket {
 	struct hlist_nulls_head chain;
-	struct hlist_nulls_head twchain;
 };
 
 /* There are a few simple rules, which allow for local port reuse by
@@ -123,7 +122,6 @@ struct inet_hashinfo {
 	 *
 	 *          TCP_ESTABLISHED <= sk->sk_state < TCP_CLOSE
 	 *
-	 * TIME_WAIT sockets use a separate chain (twchain).
 	 */
 	struct inet_ehash_bucket	*ehash;
 	spinlock_t			*ehash_locks;
@@ -318,9 +316,6 @@ static inline struct sock *inet_lookup_listener(struct net *net,
 	 net_eq(sock_net(__sk), (__net)))
 #endif /* 64-bit arch */
 
-#define INET_TW_MATCH(__sk, __net, __cookie, __saddr, __daddr, __ports, __dif)\
-	INET_MATCH(__sk, __net, __cookie, __saddr, __daddr, __ports, __dif)
-
 /*
  * Sockets in TCP_CLOSE state are _always_ taken out of the hash, so we need
  * not check it for lookups anymore, thanks Alexey. -DaveM