aria2-rust-pro/docs/perf/size-evidence.md

Size Evidence

This file records the current binary-size and code-size evidence for aria2-rust-pro in Take 2 of the modernization goal.

Commands

rtk cargo build --release -p aria2-rust-pro-cli --manifest-path .\Cargo.toml -j $env:NUMBER_OF_PROCESSORS
rtk cargo bloat --release -p aria2-rust-pro-cli --bin aria2-rust-pro --crates -n 40 -j $env:NUMBER_OF_PROCESSORS
rtk cargo rustc --release -p aria2-rust-pro-cli --bin aria2-rust-pro --manifest-path .\Cargo.toml -- --emit=llvm-ir
rtk cargo llvm-lines --files target\release\deps\aria2_rust_pro.aria2_rust_pro_cli-d4c445ae209bfe38.aria2_rust_pro_cli.b493e489391677ca-cgu.0.rcgu.o.rcgu.ll

Binary Size Snapshot

Measured on the current Windows host:

Binary	Bytes	MiB
aria2-rust-pro.exe	5,213,184	4.97
current C++ Pro Core aria2c.exe	11,412,480	10.88
upstream Windows aria2c.exe	5,649,408	5.39

Observations:

• the current Rust binary is about 54.3% smaller than the current C++ Pro Core artifact on this host
• the current Rust binary remains about 7.7% smaller than the upstream Windows aria2 binary as well
• the latest reduction came from making the release profile more artifact-shaped: codegen-units = 1, lto = "thin", and strip = "symbols"
• a later Phase 6 config-projection cleanup removed another small tranche by replacing repeated release-path BTreeMap<String, String> materialization with last-wins directive lookup on demand
• the latest checked tree, after the recent structural scheduler/DHT cleanup, leaves the release artifact at 5,213,184 bytes, up 28,672 bytes from the previous recorded snapshot rather than down
• the host artifact still stays below both checked C++ references

Cargo Bloat Summary

Current top crate contributions from cargo bloat --crates:

Crate	.text size
std	815.4 KiB
aria2_rust_pro_rpc	488.4 KiB
rustls	421.7 KiB
aria2_rust_pro_cli	246.7 KiB
aria2_rust_pro_protocol	236.3 KiB
reqwest	213.9 KiB
ring	124.2 KiB
hyper_util	107.8 KiB
hyper	104.2 KiB
aria2_rust_pro_core	100.6 KiB
tokio	94.4 KiB

Headline totals from the same run:

• .text section: about 3.6 MiB
• file size from the bloat run: about 5.0 MiB

Interpretation:

• the biggest owned size buckets are aria2_rust_pro_rpc, aria2_rust_pro_protocol, aria2_rust_pro_cli, and aria2_rust_pro_core
• the biggest third-party buckets are the HTTP/TLS stack: reqwest, rustls, hyper, hyper_util, tokio, and ring
• future size work should therefore focus on:
  • whether the default host binary really needs the full RPC/TLS surface in one always-on artifact
  • whether reqwest / rustls features can be trimmed without breaking the compatibility contract
  • whether any always-linked RPC/HTTP helpers can be split or made less eager
  • whether a future release flow should emit a stripped end-user artifact plus a separate debug-symbol artifact rather than making local release builds do both jobs at once
• within the owned CLI bucket, the same config-projection cleanup previously cut several previously ranked helpers materially in the filtered cargo bloat view:
  • run_from_env: 31.2 KiB -> 30.2 KiB
  • projection::derive_http_session: 8.6 KiB -> 5.7 KiB
  • projection::derive_runtime_config: 8.3 KiB -> 4.0 KiB
  • build_ftp_transfer_parts: 6.4 KiB -> 3.9 KiB

LLVM Lines Snapshot

Direct cargo llvm-lines --release -p aria2-rust-pro-cli --bin aria2-rust-pro currently fails on this Windows/MSVC host while linking the temporary cargo-llvm-lines crate, with many unresolved external symbols. The project itself still builds in release mode; the failure is limited to that tool's temporary relink path.

The usable current workaround is:

1. emit release LLVM IR with cargo rustc -- --emit=llvm-ir
2. point cargo llvm-lines --files at the generated CLI .ll file

That current CLI crate IR snapshot reports:

• total: 53,272 LLVM IR lines across 307 function copies
• top entries:
  • runtime_host::execute_run_invocation: 5,538 lines
  • run_from_env: 4,380 lines
  • parallel_http_runtime::execute_parallel_http_entries: 3,751 lines
  • http_runtime::execute_segment_transfers: 2,364 lines
  • http_runtime::execute_tagged_segment_transfers_with_parallelism: 2,345 lines
  • runtime_summary::collect_runtime_execution_summary: 1,207 lines

Interpretation:

• the largest CLI-side IR buckets now line up with the Phase 6 runtime and HTTP transfer paths rather than a random unrelated module
• parallel_http_runtime remains a legitimate future split/size target, but it is also the path that just delivered the latest shared-runtime performance win
• full-workspace release LLVM-lines still needs a non-MSVC or fixed cargo-llvm-lines path before it should be treated as a strict gate

Take 2 Reading

For Take 2, the honest conclusion is:

• size evidence now exists in-tree
• one real size-reduction tranche is now landed through the release profile
• the Rust host binary is now smaller than both the current C++ Pro Core and the upstream Windows binary checked on this host
• the main size pressure comes from the combined RPC + HTTP/TLS stack, not from one surprising internal crate explosion
• CLI-side LLVM IR now points at runtime execution and parallel HTTP scheduling as the next owned code-size targets
• the latest CLI IR refresh still confirms the earlier config-projection and shared-runtime cleanup reduced total CLI IR from 59,204 to 53,272 lines, but the newest structural tree should now be treated as synchronized mainly through the refreshed release build and cargo bloat --crates snapshot above
• deeper size reduction remains a future optimization lane, but the Phase 6 evidence set is now current enough to rank that work honestly