4208dbef16
In preparation for a lockless fast path in the page allocator, this change makes it so that checking if an allocation needs to be zeroed may be done atomically. Unfortunately, this means there is a CAS-loop to ensure monotonicity of the zeroedBase value in heapArena. This CAS-loop exits if an allocator acquiring memory further on in the arena wins or if it succeeds. The CAS-loop should have a relatively small amount of contention because of this monotonicity, though it would be ideal if we could just have CAS-ers with the greatest value always win. The CAS-loop is unnecessary in the steady-state, but should bring some start-up performance gains as it's likely cheaper than the additional zeroing required, especially for large allocations. For very large allocations that span arenas, the CAS-loop should be completely uncontended for most of the arenas it touches, it may only encounter contention on the first and last arena. Updates #35112. Change-Id: If3d19198b33f1b1387b71e1ce5902d39a5c0f98e Reviewed-on: https://go-review.googlesource.com/c/go/+/203859 Run-TryBot: Michael Knyszek <mknyszek@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Austin Clements <austin@google.com> |
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