[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, 7 insertions, 2 deletions

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index d84973928033..7a3bea9c28c1 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1072,11 +1072,13 @@ static int __init dccp_init(void)
         }
 
         for (i = 0; i < dccp_hashinfo.ehash_size; i++) {
-                rwlock_init(&dccp_hashinfo.ehash[i].lock);
                 INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].chain);
                 INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].twchain);
         }
 
+        if (inet_ehash_locks_alloc(&dccp_hashinfo))
+                        goto out_free_dccp_ehash;
+
         bhash_order = ehash_order;
 
         do {
@@ -1091,7 +1093,7 @@ static int __init dccp_init(void)
 
         if (!dccp_hashinfo.bhash) {
                 DCCP_CRIT("Failed to allocate DCCP bind hash table");
-                goto out_free_dccp_ehash;
+                goto out_free_dccp_locks;
         }
 
         for (i = 0; i < dccp_hashinfo.bhash_size; i++) {
@@ -1121,6 +1123,8 @@ out_free_dccp_mib:
 out_free_dccp_bhash:
         free_pages((unsigned long)dccp_hashinfo.bhash, bhash_order);
         dccp_hashinfo.bhash = NULL;
+out_free_dccp_locks:
+        inet_ehash_locks_free(&dccp_hashinfo);
 out_free_dccp_ehash:
         free_pages((unsigned long)dccp_hashinfo.ehash, ehash_order);
         dccp_hashinfo.ehash = NULL;
@@ -1139,6 +1143,7 @@ static void __exit dccp_fini(void)
         free_pages((unsigned long)dccp_hashinfo.ehash,
                    get_order(dccp_hashinfo.ehash_size *
                              sizeof(struct inet_ehash_bucket)));
+        inet_ehash_locks_free(&dccp_hashinfo);
         kmem_cache_destroy(dccp_hashinfo.bind_bucket_cachep);
         dccp_ackvec_exit();
         dccp_sysctl_exit();