Add jemalloc and jemalloc-auto features

Introduce the new features jemalloc (set jemalloc global allocator
unconditionally) and jemalloc-auto (set jemalloc global allocator on
musl-based targets to fix multithreaded performance, see [1]).

Because cargo does not support target-specific features or feature
defaults, the default is handled using a helper crate
minedmap-default-alloc.

[1] https://nickb.dev/blog/default-musl-allocator-considered-harmful-to-performance/

CHANGELOG.md

@@ -2,6 +2,28 @@
 
 ## [Unreleased] - ReleaseDate
 
+### Added
+
+- Added jemalloc support to fix performace on musl targets
+
+  The global allocator can be switched to jemalloc by enabling the `jemalloc`
+  cargo feature now. This is not the default because it is not always faster
+  than the default system allocator; in particular, the glibc allocator has
+  slightly better performance in multithreaded mode. In addition, jemalloc
+  uses a bit more memory.
+
+  In addition, the `jemalloc-auto` feature has been introduced, which is enabled
+  by default and sets the global allocator to jemalloc on platforms where it is
+  clearly advantageous. For now, this is only done on musl-based targets, as
+  musl's default allocator is very slow in multithreaded operation (which was
+  making higher thread counts like `-j8` basically useless due to 7-8x
+  slowdowns). With the new default, performance on musl is basically identical
+  to glibc.
+
+  Note that some platforms like `msvc` are unsupported by jemalloc, and trying
+  to enable the `jemalloc` feature on these platforms may break the MinedMap
+  build or cause issues at runtime.
+
 ### Changed
 
 - Unknown biome types (from not yet supported or modded versions of Minecraft)

Cargo.lock

@@ -591,6 +591,7 @@ dependencies = [
  "image",
  "indexmap",
  "lru",
+ "minedmap-default-alloc",
  "minedmap-nbt",
  "minedmap-resource",
  "minedmap-types",
@@ -608,6 +609,13 @@ dependencies = [
  "zstd",
 ]
 
+[[package]]
+name = "minedmap-default-alloc"
+version = "0.1.0"
+dependencies = [
+ "tikv-jemallocator",
+]
+
 [[package]]
 name = "minedmap-nbt"
 version = "0.1.1"
@@ -1057,6 +1065,26 @@ dependencies = [
  "once_cell",
 ]
 
+[[package]]
+name = "tikv-jemalloc-sys"
+version = "0.6.0+5.3.0-1-ge13ca993e8ccb9ba9847cc330696e02839f328f7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cd3c60906412afa9c2b5b5a48ca6a5abe5736aec9eb48ad05037a677e52e4e2d"
+dependencies = [
+ "cc",
+ "libc",
+]
+
+[[package]]
+name = "tikv-jemallocator"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4cec5ff18518d81584f477e9bfdf957f5bb0979b0bac3af4ca30b5b3ae2d2865"
+dependencies = [
+ "libc",
+ "tikv-jemalloc-sys",
+]
+
 [[package]]
 name = "tokio"
 version = "1.43.0"

Cargo.toml

@@ -47,6 +47,7 @@ git-version = "0.3.5"
 image = { version = "0.25.1", default-features = false, features = ["png", "webp"] }
 indexmap = { version = "2.0.0", features = ["serde"] }
 lru = "0.13.0"
+minedmap-default-alloc = { version = "0.1.0", path = "crates/default-alloc", optional = true }
 minedmap-nbt = { version = "0.1.1", path = "crates/nbt", default-features = false }
 minedmap-resource = { version = "0.6.0", path = "crates/resource" }
 minedmap-types = { version = "0.1.4", path = "crates/types" }
@@ -64,5 +65,7 @@ tracing-subscriber = "0.3.17"
 zstd = "0.13.0"
 
 [features]
-default = ["zlib-ng"]
+default = ["jemalloc-auto", "zlib-ng"]
+jemalloc-auto = ["dep:minedmap-default-alloc"]
+jemalloc = ["jemalloc-auto", "minedmap-default-alloc/jemalloc"]
 zlib-ng = ["minedmap-nbt/zlib-ng"]

crates/default-alloc/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "minedmap-default-alloc"
+version = "0.1.0"
+description = "Helper crate for target-specific selection of global allocator default"
+edition.workspace = true
+license.workspace = true
+readme.workspace = true
+repository.workspace = true
+
+[dependencies]
+tikv-jemallocator = { version = "0.6.0", optional = true }
+
+[target.'cfg(target_env = "musl")'.dependencies]
+tikv-jemallocator = "*"
+
+[features]
+jemalloc = ["dep:tikv-jemallocator"]

crates/default-alloc/src/lib.rs

@@ -0,0 +1,3 @@
+#[cfg(any(target_env = "musl", feature = "jemalloc"))]
+#[global_allocator]
+static GLOBAL: tikv_jemallocator::Jemalloc = tikv_jemallocator::Jemalloc;

src/main.rs

@@ -2,6 +2,9 @@
 #![warn(missing_docs)]
 #![warn(clippy::missing_docs_in_private_items)]
 
+#[cfg(feature = "jemalloc-auto")]
+extern crate minedmap_default_alloc;
+
 mod core;
 mod io;
 mod util;