[PATCH] net core: optimize netdev_create_hash()

[Wei Yang <weiyang@linux.vnet.ibm.com>]

netdev_create_hash() is divded into two steps:
1. allocate space for hash_head
2. initialize hash_head->first to NULL for each hash_head

This patch merge the two steps into one step.

When allocating the space for hash_head, it will use kzalloc() instead of
kmalloc(). Then hash_head->first is set to NULL during the allocation step,
which means it is not necessary to call INIT_HLIST_HEAD() for each hash_head.

This will:
1. reduce the code size
2. reduce the run time of iteration on initializing hash_head array
---
 net/core/dev.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index f64e439..79f0666 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6564,13 +6564,15 @@ EXPORT_SYMBOL(netdev_increment_features);
 
 static struct hlist_head *netdev_create_hash(void)
 {
-	int i;
 	struct hlist_head *hash;
 
-	hash = kmalloc(sizeof(*hash) * NETDEV_HASHENTRIES, GFP_KERNEL);
-	if (hash != NULL)
-		for (i = 0; i < NETDEV_HASHENTRIES; i++)
-			INIT_HLIST_HEAD(&hash[i]);
+	hash = kzalloc(sizeof(*hash) * NETDEV_HASHENTRIES, GFP_KERNEL);
+
+	/*
+	 * hash[i]->first is set to NULL in kzalloc()
+	 *
+	 * INIT_HLIST_HEAD(&hash[i]) is not necessary now
+	 */
 
 	return hash;
 }
-- 
1.7.5.4