[g4dpz]

Summary

The per-bundle RIB route lookup (RouteTable::find_recurse, run on every admitted and re-dispatched bundle) allocated two heap structures on every call:

• a HashSet cycle-detection trail, and
• a Vec of candidate next-hop peers.

This replaces both with inline SmallVec types so the common lookup is allocation-free:

• Trail — SmallVec<[&Eid; 4]> instead of HashSet<&Eid>. Via chains are short, so the trail is used purely as a small set (membership check, push on descent, pop on return) and the inline capacity keeps the common walk allocation-free. Cycle-detection semantics are preserved exactly.
• Peer vector — SmallVec<[(u32, &Eid); 2]> instead of Vec. The non-ECMP case resolves to zero or one peer and no longer heap-allocates. The rare ECMP branch converts to Vec via into_vec() so LookupResult::ForwardEcmp and select_peer are unchanged, keeping the diff minimal.

Adds smallvec (default features) as a direct hardy-bpa dependency; it was already present in Cargo.lock transitively, so the lock change is a single line. no_std-safe.

No public API or routing-semantics change — this is a pure internal allocation optimisation.

Testing

CI gates run locally, all green (except the storage-tests harness, which requires a live Postgres/S3 and is unrelated to this change):

• cargo fmt --check — clean
• cargo clippy --locked --all-targets --all-features -- -D warnings — zero warnings
• cargo test --locked --all-features --workspace --exclude storage-tests — all pass

The existing routing tests cover the behaviour and pass unchanged: test_recursion_loop (cycle detection), test_reflection, test_reflection_no_double, test_union_route_member_specificity, and the ECMP tests (which exercise the multi-peer path and the into_vec() conversion).

[Copilot]

🟢 Approval recommended

The localized changes preserve cycle detection, peer ordering, and ECMP behavior, with no blocking issues identified.

No open issues 🎉

What changed in this PR

Reduces common-path heap allocations in BPA route lookup without changing public APIs or routing behavior.

Changes:

• Uses inline SmallVec storage for cycle detection and candidate peers.
• Preserves ECMP results by converting multi-peer collections to Vec.
• Adds smallvec as a direct BPA dependency.

File	Description
Cargo.lock	Records BPA’s direct smallvec dependency.
bpa/​src/​routing/​table.rs	Replaces temporary collections with inline storage and updates test calls.
bpa/​src/​routing/​rib.rs	Uses the new trail type for route lookups.
bpa/​Cargo.toml	Declares the smallvec dependency.

_{Review effort: Balanced}

[ricktaylor]

Thanks Dave, we held off because routing was in a bit of flux., but this looks 👍