ipv4: Use synchronize_rcu() during trie_rebalance()

[deliverable/linux.git] / net / ipv4 / fib_trie.c

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 63c2fa7b68c4b922840fe883bd9bdf0e9a6c21c7..58ba9f4f2c92eade0c84b5b14c84e2754d0bbccb 100644 (file)
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -164,6 +164,14 @@ static struct tnode *inflate(struct trie *t, struct tnode *tn);
 static struct tnode *halve(struct trie *t, struct tnode *tn);
 /* tnodes to free after resize(); protected by RTNL */
 static struct tnode *tnode_free_head;
+static size_t tnode_free_size;
+
+/*
+ * synchronize_rcu after call_rcu for that many pages; it should be especially
+ * useful before resizing the root node with PREEMPT_NONE configs; the value was
+ * obtained experimentally, aiming to avoid visible slowdown.
+ */
+static const int sync_pages = 128;
 
 static struct kmem_cache *fn_alias_kmem __read_mostly;
 static struct kmem_cache *trie_leaf_kmem __read_mostly;
@@ -393,6 +401,8 @@ static void tnode_free_safe(struct tnode *tn)
        BUG_ON(IS_LEAF(tn));
        tn->tnode_free = tnode_free_head;
        tnode_free_head = tn;
+       tnode_free_size += sizeof(struct tnode) +
+                          (sizeof(struct node *) << tn->bits);
 }
 
 static void tnode_free_flush(void)
@@ -404,6 +414,11 @@ static void tnode_free_flush(void)
                tn->tnode_free = NULL;
                tnode_free(tn);
        }
+
+       if (tnode_free_size >= PAGE_SIZE * sync_pages) {
+               tnode_free_size = 0;
+               synchronize_rcu();
+       }
 }
 
 static struct leaf *leaf_new(void)