1b1fbb3192
Prior to this change, if the heap was very discontiguous (such as in TestArenaCollision) it's possible we could map a large amount of memory as R/W and commit it. We would use only the start and end to track what should be mapped, and we would extend that mapping as needed to accomodate a potentially fragmented address space. After this change, we only map exactly the part of the summary arrays that we need by using the inUse ranges from the previous change. This reduces the GCSys footprint of TestArenaCollision from 300 MiB to 18 MiB. Because summaries are no longer mapped contiguously, this means the scavenger can no longer iterate directly. This change also updates the scavenger to borrow ranges out of inUse and iterate over only the parts of the heap which are actually currently in use. This is both an optimization and necessary for correctness. Fixes #35514. Change-Id: I96bf0c73ed0d2d89a00202ece7b9d089a53bac90 Reviewed-on: https://go-review.googlesource.com/c/go/+/207758 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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