s3: Optimize g_lock_lock for a heavily contended case

Only check the existence of the lock owner in g_lock_parse, check the rest of
the records only when we got the lock successfully. This reduces the load on
process_exists which can involve a network roundtrip in the clustered case.

1 files changed, 36 insertions, 3 deletions

diff --git a/source3/lib/g_lock.c b/source3/lib/g_lock.c
index 42c0397189..e2620255d9 100644
--- a/source3/lib/g_lock.c
+++ b/source3/lib/g_lock.c
@@ -108,6 +108,34 @@ static bool g_lock_parse(TALLOC_CTX *mem_ctx, TDB_DATA data,
 			      (locks[i].lock_type & G_LOCK_PENDING) ?
 			      "(pending)" : "(owner)"));
 
+		if (((locks[i].lock_type & G_LOCK_PENDING) == 0)
+		    && !process_exists(locks[i].pid)) {
+
+			DEBUGADD(10, ("lock owner %s died -- discarding\n",
+				      procid_str(talloc_tos(),
+						 &locks[i].pid)));
+
+			if (i < (num_locks-1)) {
+				locks[i] = locks[num_locks-1];
+			}
+			num_locks -= 1;
+		}
+	}
+
+	*plocks = locks;
+	*pnum_locks = num_locks;
+	return true;
+}
+
+static void g_lock_cleanup(int *pnum_locks, struct g_lock_rec *locks)
+{
+	int i, num_locks;
+
+	num_locks = *pnum_locks;
+
+	DEBUG(10, ("g_lock_cleanup: %d locks\n", num_locks));
+
+	for (i=0; i<num_locks; i++) {
 		if (process_exists(locks[i].pid)) {
 			continue;
 		}
@@ -119,10 +147,8 @@ static bool g_lock_parse(TALLOC_CTX *mem_ctx, TDB_DATA data,
 		}
 		num_locks -= 1;
 	}
-
-	*plocks = locks;
 	*pnum_locks = num_locks;
-	return true;
+	return;
 }
 
 static struct g_lock_rec *g_lock_addrec(TALLOC_CTX *mem_ctx,
@@ -239,6 +265,13 @@ again:
 		locks[our_index].lock_type = lock_type;
 	}
 
+	if (NT_STATUS_IS_OK(status) && ((lock_type & G_LOCK_PENDING) == 0)) {
+		/*
+		 * Walk through the list of locks, search for dead entries
+		 */
+		g_lock_cleanup(&num_locks, locks);
+	}
+
 	data = make_tdb_data((uint8_t *)locks, num_locks * sizeof(*locks));
 	store_status = rec->store(rec, data, 0);
 	if (!NT_STATUS_IS_OK(store_status)) {