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