Reduce RSS peak during compaction (observed on CC) with userfaultfd-GC

Bug: 160737021
Test: ART_USE_READ_BARRIER=false art/test/testrunner/testrunner.py and module install
Change-Id: Idb841e59da485373cb92e8c13025e1b0a49b445a
(cherry picked from commit 6ea303f95a5806f6dea00ef34bf75bd79001bf47)
Merged-In: Idb841e59da485373cb92e8c13025e1b0a49b445a
2 files changed