Fix two battery risks in the per-app remote routing feature - #742
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Gate routing-prefs resolution on WireGuard being active: with WG off, stale wg_route_mode/wg_route prefs no longer keep fwd53's per-DNS-query UID lookup and upcall path enabled. Make the native flow-verdict cache 4-way set-associative instead of direct-mapped, so two concurrently busy flows sharing a hash no longer guarantee mutual eviction and per-packet fallback to a Binder/procfs UID lookup.
kasnder
marked this pull request as ready for review
August 20, 2026 21:43
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Summary
Reviewed the recent per-app remote (WireGuard) routing work for battery impact and found two risks, both fixed here. Both are traffic-driven, opt-in-feature costs — the shipped default (no routing overrides configured) is unaffected either way.
ServiceSinkhole.prepareUidAllowedresolvedwg_route_mode/wg_routepreferences unconditionally, so a user who had switched toselectedmode or added a per-app override, then disabled WireGuard, kept payingfwd53's per-DNS-query UID lookup, JNI upcall, and forwarded UDP session — with no tunnel left to route around. Now that state only resolves whenhasActiveWireGuard()is true; otherwise it collapses to the no-tunnel defaults (empty override set, default-tunnel, no direct DNS redirect), matching pre-feature behaviour.policy.c) was direct-mapped (1024 slots). Two concurrently active flows sharing a hash bucket evicted each other on every packet; each eviction forced a session-table walk (guaranteed futile for tunnelled flows, which never get anng_session) followed by a per-packet Binder/procfs UID lookup — the exact cost the cache exists to avoid. Replaced with a 4-way set-associative cache (256 sets × 4 ways, same ~56 KB budget), so collisions now need 5 simultaneously-hot flows sharing a set before any fallback lookup is forced.Test plan
./gradlew :app:compileGithubDebugJavaWithJavac— not run: this session's container has no Android SDK/NDK (android-envreports exit 3;gradlewfails at SDK-location configuration before compiling)../gradlew :app:testGithubDebugUnitTest— not run, same reason.assembleGithubDebug(native build) — not run, same reason.policy.candRemoteRoutingLogic.java.Recommend running the above before merge on a machine/session with the Android SDK/NDK available.
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