memory-allocator

name	memory-allocator
description	Choosing and profiling the global allocator (jemalloc, mimalloc, system) in the backend-service `service` template

Memory Allocator

The allocator choice at generation time sets the #[global_allocator] in src/main.rs. It is a build-time decision, not a runtime knob.

Which one

• jemalloc (tikv-jemallocator, the default): a mature, arena-based allocator with strong fragmentation control and steady RSS under sustained multi-threaded load, plus deep runtime tuning (MALLOC_CONF) and built-in heap profiling. The cost is a higher idle baseline and a larger binary. It does not build on MSVC, so both the dependency and the #[global_allocator] static are gated with cfg(not(target_env = "msvc")).
• mimalloc: newer and smaller, with very fast small-allocation paths and typically lower memory footprint, but far fewer tuning knobs and less of a track record under sustained server load. A strong pick for allocation-heavy workloads or a Windows-MSVC target.
• system: the platform allocator (glibc on Linux). No extra dependency and the simplest build, but glibc's per-thread arenas can grow RSS under heavy multi-threaded churn. Use it for low-concurrency services, when you want zero added dependencies, or as a baseline when isolating an allocator-sensitive bug.

jemalloc is the default; switch only after measuring your workload.

Heap profiling with dial9

When the dial9 feature is on, the global allocator is wrapped in Dial9Allocator, which is a passthrough until a memory profiler is installed in main. Set DIAL9_MEMORY_PROFILE_ENABLED=true to install it at startup and capture allocation samples. dial9's own tooling reads the resulting profile; this skill does not cover that analysis.

Invariants

• Keep the cfg(not(target_env = "msvc")) gate on both the jemalloc dependency and its static, or Windows builds break.
• There is exactly one #[global_allocator]. When dial9 is on, the allocator must be the Dial9Allocator wrapper around your chosen allocator, not the bare allocator, or heap profiling silently records nothing.

References

• jemalloc: https://docs.rs/tikv-jemallocator, mimalloc: https://docs.rs/mimalloc
• Profiling analysis and the viewer: see the dial9 references in the telemetry skill.