Macro readings_probe::wrap_global_allocator

macro_rules! wrap_global_allocator {
    ($alloc : path) => { ... };
}

Setup global allocator instrumentation, to track rust-managed memory.

It is not mandatory to do so, as we also register the RSZ and VSZ as reported by the OS, but it may be interesting. From our experience it may be worth activating it as the cost is relatively modest.

This macro allows to specify a specific allocator instance to wrap and make global (for instance, jemalloc).