Re: rib_trie / Fix inflate_threshold_root. Now=15 size=11 bits

[Jarek Poplawski <jarkao2@gmail.com>]

On Sun, Jun 28, 2009 at 01:04:51PM +0200, Robert Olsson wrote:
...
>  The memory patches and "manual RCU" are also interesting to address
>  the case with PREEMTP's.

Since 2.6.29 looks like prefered here, and there were a lot of takes
in this thread, I attach below a combined all-in-one patch including:
- 2.6.29 -> 2.6.30 preemption disable patch
- 2 RCU vs. preemption fixes from 2.6.31-rc
- "manual RCU" patch to force vfree/kfree before root's resize (take 3)
- "automatic" inflate_threshold_root fix (take 2)

Thanks,
Jarek P.

--- (for 2.6.29.x or even .28 or .27; any testing appreciated)

diff -Nurp a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
--- a/net/ipv4/fib_trie.c	2009-06-27 20:25:06.000000000 +0200
+++ b/net/ipv4/fib_trie.c	2009-06-28 15:45:02.000000000 +0200
@@ -123,6 +123,7 @@ struct tnode {
 	union {
 		struct rcu_head rcu;
 		struct work_struct work;
+		struct tnode *tnode_free;
 	};
 	struct node *child[0];
 };
@@ -161,6 +162,8 @@ static void tnode_put_child_reorg(struct
 static struct node *resize(struct trie *t, struct tnode *tn);
 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 struct kmem_cache *fn_alias_kmem __read_mostly;
 static struct kmem_cache *trie_leaf_kmem __read_mostly;
@@ -315,6 +318,7 @@ static const int halve_threshold = 25;
 static const int inflate_threshold = 50;
 static const int halve_threshold_root = 8;
 static const int inflate_threshold_root = 15;
+static int inflate_threshold_root_fix;
 
 
 static void __alias_free_mem(struct rcu_head *head)
@@ -363,6 +367,17 @@ static void __tnode_vfree(struct work_st
 	vfree(tn);
 }
 
+static void __tnode_free(struct tnode *tn)
+{
+	size_t size = sizeof(struct tnode) +
+		      (sizeof(struct node *) << tn->bits);
+
+	if (size <= PAGE_SIZE)
+		kfree(tn);
+	else
+		vfree(tn);
+}
+
 static void __tnode_free_rcu(struct rcu_head *head)
 {
 	struct tnode *tn = container_of(head, struct tnode, rcu);
@@ -385,6 +400,24 @@ static inline void tnode_free(struct tno
 		call_rcu(&tn->rcu, __tnode_free_rcu);
 }
 
+static void tnode_free_safe(struct tnode *tn)
+{
+	BUG_ON(IS_LEAF(tn));
+	tn->tnode_free = tnode_free_head;
+	tnode_free_head = tn;
+}
+
+static void tnode_free_flush(void)
+{
+	struct tnode *tn;
+
+	while ((tn = tnode_free_head)) {
+		tnode_free_head = tn->tnode_free;
+		tn->tnode_free = NULL;
+		__tnode_free(tn);
+	}
+}
+
 static struct leaf *leaf_new(void)
 {
 	struct leaf *l = kmem_cache_alloc(trie_leaf_kmem, GFP_KERNEL);
@@ -495,7 +528,7 @@ static struct node *resize(struct trie *
 
 	/* No children */
 	if (tn->empty_children == tnode_child_length(tn)) {
-		tnode_free(tn);
+		tnode_free_safe(tn);
 		return NULL;
 	}
 	/* One child */
@@ -509,7 +542,7 @@ static struct node *resize(struct trie *
 
 			/* compress one level */
 			node_set_parent(n, NULL);
-			tnode_free(tn);
+			tnode_free_safe(tn);
 			return n;
 		}
 	/*
@@ -581,7 +614,8 @@ static struct node *resize(struct trie *
 	/* Keep root node larger  */
 
 	if (!tn->parent)
-		inflate_threshold_use = inflate_threshold_root;
+		inflate_threshold_use = inflate_threshold_root +
+					inflate_threshold_root_fix;
 	else
 		inflate_threshold_use = inflate_threshold;
 
@@ -605,15 +639,22 @@ static struct node *resize(struct trie *
 	}
 
 	if (max_resize < 0) {
-		if (!tn->parent)
-			pr_warning("Fix inflate_threshold_root."
-				   " Now=%d size=%d bits\n",
-				   inflate_threshold_root, tn->bits);
-		else
+		if (!tn->parent) {
+			if (inflate_threshold_root_fix * 2 <
+			    inflate_threshold_root)
+				inflate_threshold_root_fix++;
+			else
+				pr_warning("Fix inflate_threshold_root."
+					   " Now=%d size=%d bits fix=%d\n",
+					   inflate_threshold_root, tn->bits,
+					   inflate_threshold_root_fix);
+		} else {
 			pr_warning("Fix inflate_threshold."
 				   " Now=%d size=%d bits\n",
 				   inflate_threshold, tn->bits);
-	}
+		}
+	} else if (max_resize > 4 && !tn->parent && inflate_threshold_root_fix)
+		inflate_threshold_root_fix--;
 
 	check_tnode(tn);
 
@@ -670,7 +711,7 @@ static struct node *resize(struct trie *
 			/* compress one level */
 
 			node_set_parent(n, NULL);
-			tnode_free(tn);
+			tnode_free_safe(tn);
 			return n;
 		}
 
@@ -756,7 +797,7 @@ static struct tnode *inflate(struct trie
 			put_child(t, tn, 2*i, inode->child[0]);
 			put_child(t, tn, 2*i+1, inode->child[1]);
 
-			tnode_free(inode);
+			tnode_free_safe(inode);
 			continue;
 		}
 
@@ -801,9 +842,9 @@ static struct tnode *inflate(struct trie
 		put_child(t, tn, 2*i, resize(t, left));
 		put_child(t, tn, 2*i+1, resize(t, right));
 
-		tnode_free(inode);
+		tnode_free_safe(inode);
 	}
-	tnode_free(oldtnode);
+	tnode_free_safe(oldtnode);
 	return tn;
 nomem:
 	{
@@ -885,7 +926,7 @@ static struct tnode *halve(struct trie *
 		put_child(t, newBinNode, 1, right);
 		put_child(t, tn, i/2, resize(t, newBinNode));
 	}
-	tnode_free(oldtnode);
+	tnode_free_safe(oldtnode);
 	return tn;
 nomem:
 	{
@@ -983,12 +1024,14 @@ fib_find_node(struct trie *t, u32 key)
 	return NULL;
 }
 
-static struct node *trie_rebalance(struct trie *t, struct tnode *tn)
+static void trie_rebalance(struct trie *t, struct tnode *tn)
 {
 	int wasfull;
-	t_key cindex, key = tn->key;
+	t_key cindex, key;
 	struct tnode *tp;
 
+	key = tn->key;
+
 	while (tn != NULL && (tp = node_parent((struct node *)tn)) != NULL) {
 		cindex = tkey_extract_bits(key, tp->pos, tp->bits);
 		wasfull = tnode_full(tp, tnode_get_child(tp, cindex));
@@ -1003,11 +1046,22 @@ static struct node *trie_rebalance(struc
 		tn = tp;
 	}
 
+	if (tnode_free_head) {
+		synchronize_rcu();
+		tnode_free_flush();
+	}
+
 	/* Handle last (top) tnode */
-	if (IS_TNODE(tn))
+	if (IS_TNODE(tn)) {
 		tn = (struct tnode *)resize(t, (struct tnode *)tn);
+		rcu_assign_pointer(t->trie, (struct node *)tn);
+		synchronize_rcu();
+		tnode_free_flush();
+	} else {
+		rcu_assign_pointer(t->trie, (struct node *)tn);
+	}
 
-	return (struct node *)tn;
+	return;
 }
 
 /* only used from updater-side */
@@ -1155,7 +1209,7 @@ static struct list_head *fib_insert_node
 
 	/* Rebalance the trie */
 
-	rcu_assign_pointer(t->trie, trie_rebalance(t, tp));
+	trie_rebalance(t, tp);
 done:
 	return fa_head;
 }
@@ -1575,7 +1629,7 @@ static void trie_leaf_remove(struct trie
 	if (tp) {
 		t_key cindex = tkey_extract_bits(l->key, tp->pos, tp->bits);
 		put_child(t, (struct tnode *)tp, cindex, NULL);
-		rcu_assign_pointer(t->trie, trie_rebalance(t, tp));
+		trie_rebalance(t, tp);
 	} else
 		rcu_assign_pointer(t->trie, NULL);