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Custom Memory Allocator

Overview

Ferrite uses platform-specific high-performance memory allocators to reduce heap fragmentation and improve allocation performance during long editing sessions.

  • Windows: mimalloc (Microsoft's compact, fast allocator)
  • Unix (Linux/macOS): jemalloc (battle-tested allocator from Meta/Facebook)

Key Files

File Purpose
Cargo.toml Platform-specific allocator dependencies and feature flag
src/main.rs Global allocator configuration with #[global_allocator]

Implementation Details

Feature Flag

The allocator is controlled by the high-perf-alloc feature, enabled by default:

[features]
default = ["bundle-icon", "high-perf-alloc"]
high-perf-alloc = ["mimalloc", "tikv-jemallocator"]

Platform-Specific Dependencies

[target.'cfg(windows)'.dependencies]
mimalloc = { version = "0.1", default-features = false, optional = true }

[target.'cfg(unix)'.dependencies]
tikv-jemallocator = { version = "0.6", optional = true }

Global Allocator Declaration

In src/main.rs, conditional compilation selects the appropriate allocator:

#[cfg(all(feature = "high-perf-alloc", target_os = "windows"))]
#[global_allocator]
static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;

#[cfg(all(feature = "high-perf-alloc", unix))]
#[global_allocator]
static GLOBAL: tikv_jemallocator::Jemalloc = tikv_jemallocator::Jemalloc;

Dependencies Used

Crate Version Platform Purpose
mimalloc 0.1 Windows Microsoft's high-performance allocator
tikv-jemallocator 0.6 Unix jemalloc wrapper (TiKV's maintained fork)

Benefits

  1. Reduced fragmentation: Better memory reuse over long sessions
  2. Faster allocations: Optimized for small allocations (common in text editors)
  3. Thread-local caches: Reduced lock contention on multi-threaded operations
  4. Consistent performance: Less variance in allocation latency

Trade-offs

  • Slightly higher baseline memory (~1-3MB overhead for allocator metadata)
  • Benefits most visible with sustained use and many open/close cycles

Usage

Default Build (with allocator)

cargo build --release

Build Without Allocator

cargo build --release --no-default-features --features bundle-icon

Verify Allocator on Linux

# jemalloc should be statically linked, but you can check symbols:
nm target/release/ferrite | grep -i jemalloc

Notes

  • Uses tikv-jemallocator instead of the deprecated jemallocator crate
  • Allocators are statically linked (no runtime DLL dependencies)
  • CI builds automatically use the appropriate allocator per platform