runtime: flush each idle P's page cache at the end of each GC cycle
Currently pages may linger in an idle P's page cache, hiding the memory
from the scavenger precisely when it's useful to return memory to the OS
and reduce the application's footprint.
Change-Id: I49fbcd806b6c66991d1ca87949f76a9f06708e70
Reviewed-on: https://go-review.googlesource.com/c/go/+/453622
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>