Crate mod_alloc 

mod-alloc

Allocation profiling for Rust. Tracks allocation counts, total bytes, peak resident memory, and current resident memory by wrapping the system allocator via GlobalAlloc.

Designed as a lean replacement for dhat with MSRV 1.75 and zero external dependencies on the hot path.

Installing as the global allocator

use mod_alloc::{ModAlloc, Profiler};

#[global_allocator]
static GLOBAL: ModAlloc = ModAlloc::new();

fn main() {
    let p = Profiler::start();

    let v: Vec<u64> = (0..1000).collect();
    drop(v);

    let stats = p.stop();
    println!("Allocations: {}", stats.alloc_count);
    println!("Total bytes: {}", stats.total_bytes);
    println!("Peak bytes (absolute): {}", stats.peak_bytes);
}

Counter semantics

The four Tier 1 counters track allocator activity since the installed ModAlloc began counting (or since the last ModAlloc::reset call):

Counter	Updated on alloc	Updated on dealloc
alloc_count	+= 1	(unchanged)
total_bytes	+= size	(unchanged)
current_bytes	+= size	-= size
peak_bytes	high-water mark of current	(unchanged)

realloc is counted as one allocation event. total_bytes increases by the growth delta on a growing realloc and is unchanged on a shrinking realloc.

Status

v0.9.1 adds Tier 2 (inline backtrace capture) behind the backtraces feature. Default builds still ship Tier 1 counters only. Tier 3 (DHAT-compatible JSON output) lands in v0.9.3.

Backtraces (backtraces feature)

With mod-alloc = { version = "0.9", features = ["backtraces"] } and RUSTFLAGS="-C force-frame-pointers=yes", each tracked allocation captures up to 8 frames of its call site via inline frame-pointer walking on x86_64 and aarch64. Per-call-site aggregation is exposed via ModAlloc::call_sites (available only with the backtraces feature); the result is raw return addresses. Symbolication ships in v0.9.2.

Aggregation-table size is controlled by the MOD_ALLOC_BUCKETS environment variable at process start (default 4,096 buckets, ~384 KB).

Structs

AllocStats

Snapshot of allocation statistics at a point in time.

CallSiteStatsbacktraces

One row in the per-call-site report.

ModAlloc

Global allocator wrapper that tracks allocations.

Profiler

Scoped profiler that captures a delta between start and stop.

SymbolicatedCallSitesymbolicate

One symbolicated call site (counterpart of CallSiteStats).

SymbolicatedFramesymbolicate

One symbolicated frame within a call site.