Answers a question the existing tooling could not: of everything we
allocate, how much is never used?
Lanes, all driven by scripts/memwaste.sh:
event every allocation observed through the memory core — size, age,
churn, and whether the bytes were ever written
access SanitizerCoverage load/store instrumentation, so "allocated and
never touched" is measured rather than inferred
scaling k vs 2k replicas through clang profile counters, to catch
super-linear work per file
padding allocator slack per size class
ratchet the numbers recorded per venue so a regression is visible
The event lane needed a foreign-free counter: on Windows the override sees
frees for blocks it never allocated (they come from the CRT), and counting
those as untracked tripped the soundness gate. mem_events now separates
them (14 daemon / 5 worker on the Go corpus).
Two portability fixes the lanes surfaced, both real:
- the enable decision must not be cached before `environ` exists. Under
-fsanitize-coverage the UBSan preinit runs dlsym -> malloc -> our
wrapper before glibc sets up environ, so the lane silently disabled
itself and produced no dump at all on Linux.
- the access map needs 48 bits: arm64 Linux hands out addresses above
2^47, which a 47-bit map dropped on the floor.
mem_profile is retired into this: it measured a strict subset and had its
own sampling story.
Local-only by decision — not a PR-CI gate. _memwaste.yml runs the lanes on
all three platforms report-only, and pr.yml/release.yml carry the wiring.
Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
