Use mimalloc for benchmarks (#7029)

`mimalloc` is a _much_ faster allocator, especially important when doing
a lot of small allocations (which egui does).

We use `mimalloc` in Rerun, and I recommend everyone to use it.

## The difference it makes

![image](https://github.com/user-attachments/assets/b22e0025-bc5e-4b3c-94e0-74ce46e86f85)

Cargo.lock

@@ -1336,6 +1336,7 @@ dependencies = [
  "env_logger",
  "image",
  "log",
+ "mimalloc",
  "poll-promise",
  "profiling",
  "puffin",
@@ -1358,6 +1359,7 @@ dependencies = [
  "egui",
  "egui_extras",
  "egui_kittest",
+ "mimalloc",
  "rand",
  "serde",
  "unicode_names2",
@@ -1559,6 +1561,7 @@ dependencies = [
  "emath",
  "epaint_default_fonts",
  "log",
+ "mimalloc",
  "nohash-hasher",
  "parking_lot",
  "profiling",
@@ -2486,6 +2489,16 @@ version = "0.2.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8355be11b20d696c8f18f6cc018c4e372165b1fa8126cef092399c9951984ffa"
 
+[[package]]
+name = "libmimalloc-sys"
+version = "0.1.42"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec9d6fac27761dabcd4ee73571cdb06b7022dc99089acbe5435691edffaac0f4"
+dependencies = [
+ "cc",
+ "libc",
+]
+
 [[package]]
 name = "libredox"
 version = "0.1.3"
@@ -2591,6 +2604,15 @@ dependencies = [
  "paste",
 ]
 
+[[package]]
+name = "mimalloc"
+version = "0.1.46"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "995942f432bbb4822a7e9c3faa87a695185b0d09273ba85f097b54f4e458f2af"
+dependencies = [
+ "libmimalloc-sys",
+]
+
 [[package]]
 name = "mime"
 version = "0.3.17"

Cargo.toml

@@ -87,6 +87,7 @@ home = "0.5.9"
 image = { version = "0.25", default-features = false }
 kittest = { version = "0.1.0", git = "https://github.com/rerun-io/kittest", branch = "main" }
 log = { version = "0.4", features = ["std"] }
+mimalloc = "0.1.46"
 nohash-hasher = "0.2"
 parking_lot = "0.12"
 pollster = "0.4"

crates/egui/src/lib.rs

@@ -400,6 +400,9 @@
 //! profile-with-puffin = ["profiling/profile-with-puffin"]
 //! ```
 //!
+//! ## Custom allocator
+//! egui apps can run significantly (~20%) faster by using a custom allocator, like [mimalloc](https://crates.io/crates/mimalloc) or [talc](https://crates.io/crates/talc).
+//!
 
 #![allow(clippy::float_cmp)]
 #![allow(clippy::manual_range_contains)]

crates/egui_demo_app/Cargo.toml

@@ -86,6 +86,7 @@ env_logger = { version = "0.10", default-features = false, features = [
   "auto-color",
   "humantime",
 ] }
+mimalloc.workspace = true
 rfd = { version = "0.15.3", optional = true }
 
 # web:

crates/egui_demo_app/src/main.rs

@@ -4,6 +4,9 @@
 #![allow(rustdoc::missing_crate_level_docs)] // it's an example
 #![allow(clippy::never_loop)] // False positive
 
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc; // Much faster allocator, can give 20% speedups: https://github.com/emilk/egui/pull/7029
+
 // When compiling natively:
 fn main() -> eframe::Result {
     for arg in std::env::args().skip(1) {

crates/egui_demo_lib/Cargo.toml

@@ -56,8 +56,9 @@ serde = { workspace = true, optional = true }
 
 [dev-dependencies]
 criterion.workspace = true
-egui_kittest = { workspace = true, features = ["wgpu", "snapshot"] }
 egui = { workspace = true, features = ["default_fonts"] }
+egui_kittest = { workspace = true, features = ["wgpu", "snapshot"] }
+mimalloc.workspace = true                                            # for benchmarks
 rand = "0.9"
 
 [[bench]]

crates/egui_demo_lib/benches/benchmark.rs

@@ -8,6 +8,9 @@ use egui::{Button, Id, RichText, TextureId, Ui, UiBuilder, Vec2};
 use egui_demo_lib::LOREM_IPSUM_LONG;
 use rand::Rng as _;
 
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc; // Much faster allocator
+
 /// Each iteration should be called in their own `Ui` with an intentional id clash,
 /// to prevent the Context from building a massive map of `WidgetRects` (which would slow the test,
 /// causing unreliable results).

crates/epaint/Cargo.toml

@@ -101,6 +101,7 @@ backtrace = { workspace = true, optional = true }
 
 [dev-dependencies]
 criterion.workspace = true
+mimalloc.workspace = true
 similar-asserts.workspace = true
 
 

crates/epaint/benches/benchmark.rs

@@ -5,6 +5,9 @@ use epaint::{
     TessellationOptions, Tessellator, TextureAtlas, Vec2,
 };
 
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc; // Much faster allocator
+
 fn single_dashed_lines(c: &mut Criterion) {
     c.bench_function("single_dashed_lines", move |b| {
         b.iter(|| {