ipv4: Use synchronize_rcu() during trie_rebalance() (c3059477) · Commits · 戴 / test

During trie_rebalance() we free memory after resizing with call_rcu(), but large updates, especially with PREEMPT_NONE configs, can cause memory stresses, so this patch calls synchronize_rcu() in tnode_free_flush() after each sync_pages to guarantee such freeing (especially before resizing the root node). The value of sync_pages = 128 is based on Pawel Staszewski's tests as the lowest which doesn't hinder updating times. (For testing purposes there was a sysfs module parameter to change it on demand, but it's removed until we're sure it could be really useful.) The patch is based on suggestions by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reported-by:

Pawel Staszewski <pstaszewski@itcare.pl> Tested-by:

Pawel Staszewski <pstaszewski@itcare.pl> Signed-off-by:

Jarek Poplawski <jarkao2@gmail.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -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)

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