Tracking issue for rust-lang/rfcs#1183 rust-lang/rfcs#1974

Known bugs:

• The #[global_allocator] attribute doesn't work in modules global_allocator can not not be defined inside module #44113

Current status:

• Implemented in rustc: Implement the #[global_allocator] attribute #42727
• Stabilization checklist
  • Remove docs from the unstable book
  • Add docs to the real book
• Add jemalloc as a crates on crates.io (jemallocator)
• Once stable, link binaries to the system allocator by default Switch the default global allocator to System, remove alloc_jemalloc, use jemallocator in rustc #36963
  • known issues Switch the default global allocator to System, remove alloc_jemalloc, use jemallocator in rustc #36963 (comment)
  • valgrind doesn't work on jemalloc Valgrind doesn't report allocations with jemalloc on nightly #28224
  • crates are gone Tracking issue for alloc_system/alloc_jemalloc #33082

A quick summary of the current state of this feature is that you can change the default global allocator via:

// Change this program's global allocator. At most one `#[global_allocator]` 
// allowed in any crate graph.
#[global_allocator]
static ALLOCATOR: MyAlloc = MyAlloc;
// When defining a global allocator, the `Alloc` trait must be defined
// for `&'a T` instead of `T`
use std::heap::Alloc;
struct MyAlloc;
impl<'a> Alloc for &'a MyAlloc {
    // ...
}