GitLab

This may improve perormance during concurrent access
to mheap.central array from multiple CPU cores.

Change-Id: I8f48dd2e72aa62e9c32de07ae60fe552d8642782
Reviewed-on: https://go-review.googlesource.com/41550

Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>