V8's old-space major GC has a sweeping phase that runs concurrently after marking completes. A developer notices that immediately after a full GC, process RSS does not drop even though heapUsed fell sharply. From how mark-sweep (without full compaction) and the OS interact, what best explains the unchanged RSS?
// after a major GC:
// process.memoryUsage().heapUsed -> dropped a lot
// process RSS -> roughly unchanged