alloc-tracker

# Memory Profiling with alloc\_tracker Use the [alloc\_tracker](https://crates.io/crates/alloc_tracker) crate to measure per-phase allocation statistics. This is useful for identifying which phases of the pipeline allocate the most memory. Note: the numbers are cumulative allocations (not peak live memory). Use `/usr/bin/time -v` to measure peak RSS, or `just heaptrack` for detailed heap profiling. Note: print to stderr (`eprint!`), not stdout, since stdout carries the OCI archive. ## 1. Add the dependency (feature-gated) In `Cargo.toml`: ```toml [features] alloc_tracker = ["dep:alloc_tracker"] [dependencies] alloc_tracker = { version = "0.5", optional = true } ``` ## 2. Register the global allocator In `src/main.rs` (after imports): ```rust #[cfg(feature = "alloc_tracker")] #[global_allocator] static ALLOCATOR: alloc_tracker::Allocator<std::alloc::System> = alloc_tracker::Allocator::system(); ``` ## 3. Instrument phases in cmd\_build In `src/cmd_build.rs`, create a session and wrap phases in spans: ```rust #[cfg(feature = "alloc_tracker")] let alloc_session = alloc_tracker::Session::new(); let files = { #[cfg(feature = "alloc_tracker")] let _span = alloc_session.operation("scan").measure_process(); // ... scan code ... }; // ... repeat for components, packing, oci_build ... #[cfg(feature = "alloc_tracker")] eprint!("{}", alloc_session.to_report()); ``` ## 4. Build and run ```bash just buildimg --no-chunk --features alloc_tracker just split $IMG ``` This prints a table like: ```text | Operation | Mean bytes | Mean count | |------------|------------|------------| | components | 252055871 | 1049679 | | oci_build | 29006550 | 1106100 | | packing | 9073500 | 3033 | | scan | 99375505 | 607710 | ``` ## 5. Clean up Remove the `alloc_tracker` dependency, feature, global allocator, and instrumentation spans before committing. These are for local investigation only.