390ffce7d6
CL 614257 refactored mallocgc but lost an optimization: if a span for a
large object is already backed by memory fresh from the OS (and thus
zeroed), we don't need to zero it. CL 614257 unconditionally zeroed
spans for large objects that contain pointers.
This change restores the optimization from before CL 614257, which seems
to matter in some real-world programs.
While we're here, let's also fix a hole with the garbage collector being
able to observe uninitialized memory of the large object is observed
by the conservative scanner before being published. The gory details are
in a comment in heapSetTypeLarge. In short, this change makes
span.largeType an atomic variable, such that the GC can only observe
initialized memory if span.largeType != nil.
For #72991.
Fixes #73800.
Change-Id: I2048aeb220ab363d252ffda7d980b8788e9674dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/659956
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>
(cherry picked from commit df9888ea4e)
Reviewed-on: https://go-review.googlesource.com/c/go/+/682356
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