netfilter: nf_conntrack: use SLAB_DESTROY_BY_RCU and get rid of call_rcu()

Use "hlist_nulls" infrastructure we added in 2.6.29 for RCUification of UDP & TCP.

This permits an easy conversion from call_rcu() based hash lists to a
SLAB_DESTROY_BY_RCU one.

Avoiding call_rcu() delay at nf_conn freeing time has numerous gains.

First, it doesnt fill RCU queues (up to 10000 elements per cpu).
This reduces OOM possibility, if queued elements are not taken into account
This reduces latency problems when RCU queue size hits hilimit and triggers
emergency mode.

- It allows fast reuse of just freed elements, permitting better use of
CPU cache.

- We delete rcu_head from "struct nf_conn", shrinking size of this structure
by 8 or 16 bytes.

This patch only takes care of "struct nf_conn".
call_rcu() is still used for less critical conntrack parts, that may
be converted later if necessary.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 3 insertions, 2 deletions

diff --git a/include/net/netns/conntrack.h b/include/net/netns/conntrack.h
index f4498a62881..9dc58402bc0 100644
--- a/include/net/netns/conntrack.h
+++ b/include/net/netns/conntrack.h
@@ -2,6 +2,7 @@
 #define __NETNS_CONNTRACK_H
 
 #include <linux/list.h>
+#include <linux/list_nulls.h>
 #include <asm/atomic.h>
 
 struct ctl_table_header;
@@ -10,9 +11,9 @@ struct nf_conntrack_ecache;
 struct netns_ct {
 	atomic_t		count;
 	unsigned int		expect_count;
-	struct hlist_head	*hash;
+	struct hlist_nulls_head	*hash;
 	struct hlist_head	*expect_hash;
-	struct hlist_head	unconfirmed;
+	struct hlist_nulls_head	unconfirmed;
 	struct ip_conntrack_stat *stat;
 #ifdef CONFIG_NF_CONNTRACK_EVENTS
 	struct nf_conntrack_ecache *ecache;