gocore: ignore unmapped parts of spans

If part of a span is not backed by physical memory (because it hasn't been
touched yet, or it has been MADV_DONTNEEDed), don't count that part
toward space used.

Change-Id: I35db31f5ea56b6fdb0d6d652dc7f1763f75c28a8
Reviewed-on: https://go-review.googlesource.com/106117
Reviewed-by: Heschi Kreinick <heschi@google.com>
1 file changed