rustfs-mimalloc

High-performance mimalloc V3 global allocator for Rust.

Overview

rustfs-mimalloc provides safe, ergonomic Rust bindings to Microsoft’s mimalloc V3 memory allocator (v3.5.0). Drop-in replacement for the system allocator with excellent multi-threaded performance.

Why this crate?

• V3 only — exclusively targets mimalloc V3, no multi-version complexity
• Always aligned — uses mi_malloc_aligned for all allocations, preventing alignment bugs
• Zero indirection — #[inline(always)] hot path, no intermediate function calls
• Cross-platform — Linux, macOS, Windows, ARM, RISC-V, musl
• Comprehensive API — stats, options, heap/arena management
• Issue-informed — addresses 40+ known issues from the reference implementation

Quick Start

[dependencies]
rustfs-mimalloc = "0.5.1"

use rustfs_mimalloc::MiMalloc;

#[global_allocator]
static GLOBAL: MiMalloc = MiMalloc;

fn main() {
    let v = vec![1, 2, 3, 4, 5];
    println!("{:?}", v);
}

Features

Feature	Default	Description
secure		Heap allocation encryption (MI_SECURE=4)
debug		mimalloc debug checks
debug_in_debug		Auto-enable debug in Cargo debug builds
override		Override system malloc/free
local_dynamic_tls		Use local-dynamic TLS model (fixes polars compatibility)
no_thp		Disable Transparent Huge Pages on Linux/Android

All stats, options, heap, and arena APIs are available without any feature flag.

API

Global Allocator

use rustfs_mimalloc::MiMalloc;

#[global_allocator]
static GLOBAL: MiMalloc = MiMalloc;

Implements GlobalAlloc with alloc, alloc_zeroed, dealloc, realloc — all using mi_malloc_aligned for guaranteed alignment.

Statistics & Diagnostics

use rustfs_mimalloc::MiMalloc;
use rustfs_mimalloc_sys::mi_option_t;

// Version: 30500 = V3.5.0
let version = MiMalloc::version();

// Stats as JSON
let json = MiMalloc::stats_json();

// Stats in human-readable text
let text = MiMalloc::stats_print();

// Process memory info (struct)
let info = MiMalloc::process_info();
println!("Peak RSS: {} bytes", info.peak_rss);

// Process memory info (text)
let text = MiMalloc::process_info_print();

// Reset stats
MiMalloc::stats_reset();

Runtime Options

use rustfs_mimalloc::MiMalloc;
use rustfs_mimalloc_sys::mi_option_t;

// Return memory to OS immediately (default delay: 10ms)
MiMalloc::option_set(mi_option_t::mi_option_purge_delay, 0);

// Read an option
let delay = MiMalloc::option_get(mi_option_t::mi_option_purge_delay);

// Toggle
MiMalloc::option_enable(mi_option_t::mi_option_show_errors);
MiMalloc::option_disable(mi_option_t::mi_option_show_errors);

Threadpool Hint

rustfs_mimalloc::set_current_thread_in_threadpool();

Call this from custom thread-pool worker threads to tell mimalloc that the current thread can run arbitrary tasks. This is a thin wrapper around mimalloc V3’s mi_thread_set_in_threadpool() API.

Heap Management

use rustfs_mimalloc::heap::Heap;

// Create a custom heap
let heap = Heap::new().expect("failed to create heap");

// Allocate from it
unsafe {
    let ptr = heap.malloc(128);
    core::ptr::write_bytes(ptr, 0xAB, 128);
    rustfs_mimalloc_sys::mi_free(ptr as *mut core::ffi::c_void);
}

// Delete heap (moves live blocks to main heap)
heap.delete();

Arena Management

use rustfs_mimalloc::heap;

// Reserve a memory arena
let arena = heap::reserve_os_memory(1024 * 1024 * 64, true, true, true)
    .expect("failed to reserve arena");

// Create a heap in the arena
let heap = heap::Heap::new_in_arena(arena).expect("failed to create heap");

Comparison with mimalloc crate

Aspect	rustfs-mimalloc	mimalloc crate
mimalloc version	V3 only (v3.5.0)	V2/V3 (configurable)
Alignment	Always aligned	Conditional
TLS model	Configurable	Forced initial-exec
Stats API	JSON + text + struct	JSON only
Options API	Full get/set/enable/disable	Partial
Heap API	Full (create/delete/destroy/alloc)	Basic
Arena API	Full (reserve/manage)	Basic
MSRV	1.96.0	1.46.0

Design Decisions

V3 Only

This crate exclusively targets mimalloc V3. Key improvements over V2:

• Metadata separated from heap objects (better cache behavior)
• Improved arena management with exclusive arenas
• Guard page support for debugging
• Theap (thread-local heap) API for fine-grained control
• Better multi-threaded performance

Always Use Aligned Allocation

All GlobalAlloc methods call mi_malloc_aligned / mi_realloc_aligned internally. Previous implementations tried to skip aligned calls for small alignments, causing alignment bugs and crashes. The overhead of always using aligned allocation is negligible.

No TLS Model Override by Default

The -ftls-model=initial-exec flag breaks compatibility with some projects (e.g., polars). Use the local_dynamic_tls feature to opt-in.

Platform Support

OS	Architecture	Status
Linux	x86_64, aarch64, arm, riscv64	✅ Tested in CI
macOS	x86_64, aarch64	✅ Tested in CI
Windows	x86_64, aarch64	✅ Tested in CI
FreeBSD	x86_64	✅ Should work
Linux (musl)	x86_64	✅ Tested in CI

Minimum Supported Rust Version

Rust 1.96.0 (2026-05-28). This crate follows a rolling support window for the latest three stable Rust release trains. With Rust 1.98.0 as the current stable release, the supported window is 1.96.x through 1.98.x.

The MSRV is tested in CI and will not change without a minor version bump.

License

Licensed under the Apache License, Version 2.0. See LICENSE.

The mimalloc C library is licensed under the MIT License. See rustfs-mimalloc-sys/c_src/mimalloc/LICENSE.

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