Use jemalloc

Benchmark #1: ./fd-sys-alloc '[0-9]\.jpg$' /home/shark
  Time (mean ± σ):     246.8 ms ±   3.4 ms    [User: 960.1 ms, System: 810.0 ms]
  Range (min … max):   244.1 ms … 257.1 ms    12 runs

Benchmark #2: ./fd-jemalloc '[0-9]\.jpg$' /home/shark
  Time (mean ± σ):     201.0 ms ±   3.0 ms    [User: 833.9 ms, System: 666.9 ms]
  Range (min … max):   196.1 ms … 206.9 ms    14 runs

Summary
  './fd-jemalloc '[0-9]\.jpg$' /home/shark' ran
    1.23 ± 0.03 times faster than './fd-sys-alloc '[0-9]\.jpg$' /home/shark'

Cargo.toml

@@ -44,6 +44,7 @@ ctrlc = "3.1"
 humantime = "1.1.1"
 lscolors = "0.6"
 globset = "0.4"
+jemallocator = "0.3.0"
 
 [dependencies.clap]
 version = "2.31.2"

src/main.rs

@@ -35,6 +35,10 @@ use crate::internal::{
     pattern_has_uppercase_char, transform_args_with_exec, FileTypes,
 };
 
+// We use jemalloc for performance reasons, see https://github.com/sharkdp/fd/pull/480
+#[global_allocator]
+static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
+
 fn main() {
     let checked_args = transform_args_with_exec(env::args_os());
     let matches = app::build_app().get_matches_from(checked_args);