wireguard: allowedips: remove nodes in O(1)
Previously, deleting peers would require traversing the entire trie in order to rebalance nodes and safely free them. This meant that removing 1000 peers from a trie with a half million nodes would take an extremely long time, during which we're holding the rtnl lock. Large-scale users were reporting 200ms latencies added to the networking stack as a whole every time their userspace software would queue up significant removals. That's a serious situation. This commit fixes that by maintaining a double pointer to the parent's bit pointer for each node, and then using the already existing node list belonging to each peer to go directly to the node, fix up its pointers, and free it with RCU. This means removal is O(1) instead of O(n), and we don't use gobs of stack. The removal algorithm has the same downside as the code that it fixes: it won't collapse needlessly long runs of fillers. We can enhance that in the future if it ever becomes a problem. This commit documents that limitation with a TODO comment in code, a small but meaningful improvement over the prior situation. Currently the biggest flaw, which the next commit addresses, is that because this increases the node size on 64-bit machines from 60 bytes to 68 bytes. 60 rounds up to 64, but 68 rounds up to 128. So we wind up using twice as much memory per node, because of power-of-two allocations, which is a big bummer. We'll need to figure something out there. Fixes: e7096c13 ("net: WireGuard secure network tunnel") Cc: stable@vger.kernel.org Signed-off-by:Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
parent
46cfe8ee