[INET]: Remove per bucket rwlock in tcp/dccp ehash table.

As done two years ago on IP route cache table (commit
22c047ccbc68fa8f3fa57f0e8f906479a062c426) , we can avoid using one
lock per hash bucket for the huge TCP/DCCP hash tables.

On a typical x86_64 platform, this saves about 2MB or 4MB of ram, for
litle performance differences. (we hit a different cache line for the
rwlock, but then the bucket cache line have a better sharing factor
among cpus, since we dirty it less often). For netstat or ss commands
that want a full scan of hash table, we perform fewer memory accesses.

Using a 'small' table of hashed rwlocks should be more than enough to
provide correct SMP concurrency between different buckets, without
using too much memory. Sizing of this table depends on
num_possible_cpus() and various CONFIG settings.

This patch provides some locking abstraction that may ease a future
work using a different model for TCP/DCCP table.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 4 deletions

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index dc429b6b0ba6..b0170732b5e9 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -747,13 +747,14 @@ skip_listen_ht:
 
         for (i = s_i; i < hashinfo->ehash_size; i++) {
                 struct inet_ehash_bucket *head = &hashinfo->ehash[i];
+                rwlock_t *lock = inet_ehash_lockp(hashinfo, i);
                 struct sock *sk;
                 struct hlist_node *node;
 
                 if (i > s_i)
                         s_num = 0;
 
-                read_lock_bh(&head->lock);
+                read_lock_bh(lock);
                 num = 0;
                 sk_for_each(sk, node, &head->chain) {
                         struct inet_sock *inet = inet_sk(sk);
@@ -769,7 +770,7 @@ skip_listen_ht:
                             r->id.idiag_dport)
                                 goto next_normal;
                         if (inet_csk_diag_dump(sk, skb, cb) < 0) {
-                                read_unlock_bh(&head->lock);
+                                read_unlock_bh(lock);
                                 goto done;
                         }
 next_normal:
@@ -791,14 +792,14 @@ next_normal:
                                     r->id.idiag_dport)
                                         goto next_dying;
                                 if (inet_twsk_diag_dump(tw, skb, cb) < 0) {
-                                        read_unlock_bh(&head->lock);
+                                        read_unlock_bh(lock);
                                         goto done;
                                 }
 next_dying:
                                 ++num;
                         }
                 }
-                read_unlock_bh(&head->lock);
+                read_unlock_bh(lock);
         }
 
 done: