This commit extends our inbound eviction protection to I2P peers to
favorise the diversity of peer connections, as peers connected
through the I2P network are otherwise disadvantaged by our eviction
criteria for their higher latency (higher min ping times) relative
to IPv4 and IPv6 peers, as well as relative to Tor onion peers.
The `networks` array is order-dependent in the case of a tie in
candidate counts between networks (earlier array members receive
priority in the case of a tie).
Therefore, we place I2P candidates before localhost and onion ones
in terms of opportunity to recover unused remaining protected slots
from the previous iteration, guesstimating that most nodes allowing
both onion and I2P inbounds will have more onion peers, followed by
localhost, then I2P, as I2P support is only being added in the
upcoming v22.0 release.
with a more abstract framework to allow easily extending inbound
eviction protection to peers connected through new higher-latency
networks that are disadvantaged by our inbound eviction criteria,
such as I2P and perhaps other BIP155 networks in the future like
CJDNS. This is a change in behavior.
The algorithm is a basically a multi-pass knapsack:
- Count the number of eviction candidates in each of the disadvantaged
privacy networks.
- Sort the networks from lower to higher candidate counts, so that
a network with fewer candidates will have the first opportunity
for any unused slots remaining from the previous iteration. In
the case of a tie in candidate counts, priority is given by array
member order from first to last, guesstimated to favor more unusual
networks.
- Iterate through the networks in this order. On each iteration,
allocate each network an equal number of protected slots targeting
a total number of candidates to protect, provided any slots remain
in the knapsack.
- Protect the candidates in that network having the longest uptime,
if any in that network are present.
- Continue iterating as long as we have non-allocated slots
remaining and candidates available to protect.
Localhost peers are treated as a network like Tor or I2P by aliasing
them to an unused Network enumerator: Network::NET_MAX.
The goal is to favorise diversity of our inbound connections.
Credit to Vasil Dimov for improving the algorithm from single-pass
to multi-pass to better allocate unused protection slots.
Co-authored-by: Vasil Dimov <vd@FreeBSD.org>
as we are about the change the behavior sufficiently that when we
have multiple disadvantaged networks and a small number of peers
under test, the number of protected peers per network can be different.
This speeds up the test significantly, which helps when
running it repeatedly.
Suggest reviewing the diff with:
colorMoved = dimmed-zebra
colorMovedWs = allow-indentation-change
Now that we have a reliable way to detect inbound onion peers, this commit
updates our existing eviction protection of 1/4 localhost peers to instead
protect up to 1/4 onion peers (connected via our tor control service), sorted by
longest uptime. Any remaining slots of the 1/4 are then allocated to protect
localhost peers, or 2 localhost peers if no slots remain and 2 or more onion
peers are protected, sorted by longest uptime.
The goal is to avoid penalizing onion peers, due to their higher min ping times
relative to IPv4 and IPv6 peers, and improve our diversity of peer connections.
Thank you to Gregory Maxwell, Suhas Daftuar, Vasil Dimov and Pieter Wuille
for valuable review feedback that shaped the direction.
and an `m_is_onion` struct member to NodeEvictionCandidate and tests.
We'll use these in the peer eviction logic to protect inbound onion peers
in addition to the existing protection of localhost peers.
An unordered set can tell if an element is present in ~O(1) time (constant on
average, worst case linear to the size of the container), which speeds up and
simplifies the lookup in IsEvicted().
Co-authored-by: Vasil Dimov <vd@FreeBSD.org>
out of net_tests, because the eviction tests:
- are a different domain of test coverage, with different dependencies
- run more slowly than the net tests
- will be growing in size, in this PR branch and in the future, as eviction
test coverage is improved
