Switch drbbdup's per-block bookkeeping to use unreachable heap instead of reachable. This data can really add up, taking up half a GB or more on large applications -- which really eats into or exceeds the limited reachable space.
Quick small local test: Before:
Basic block fragments generated : 5169
Trace fragments generated : 527
Peak vmm blocks for unreachable heap : 641
Peak vmm blocks for reachable heap : 336
After:
Basic block fragments generated : 5169
Trace fragments generated : 527
Peak vmm blocks for unreachable heap : 757
Peak vmm blocks for reachable heap : 230
Issue: #5411 (closed)