Increase in memory overhead

We are seeing a ~20% increase in memory overhead coming in build 4546. Looks like the following commit, which reverts an older commit, is the issue:

http://172.23.123.43:8000/getchangelog?product=couchbase-server&fromb=6.5.0-4545&tob=6.5.0-4546

https://github.com/couchbase/kv_engine/commit/380547e6626ac7e696f75419cf9ae613b00600ef

https://issues.couchbase.com/browse/MB-36301

4558 - http://perf.jenkins.couchbase.com/job/ares/10794/ - 42

4547 - http://perf.jenkins.couchbase.com/job/ares/10843/ - 43

4546 - http://perf.jenkins.couchbase.com/job/ares/10851/ - 42

4545 - http://perf.jenkins.couchbase.com/job/ares/10852/ - 36

4544 - http://perf.jenkins.couchbase.com/job/ares/10853/ - 35

4543 - http://perf.jenkins.couchbase.com/job/ares/10854/ - 36

4542 - http://perf.jenkins.couchbase.com/job/ares/10847/ - 35

4537 - http://perf.jenkins.couchbase.com/job/ares/10837/ - 37

4515 - http://perf.jenkins.couchbase.com/job/ares/10838/ - 38

4493 - http://perf.jenkins.couchbase.com/job/ares/10839/ - 36

4471 - http://perf.jenkins.couchbase.com/job/ares/10816/ - 35

Builds:

4546 - http://perf.jenkins.couchbase.com/job/ares/10851/ - 42

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10851/172.23.133.11.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10851/172.23.133.12.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10851/172.23.133.13.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10851/172.23.133.14.zip

4545 - http://perf.jenkins.couchbase.com/job/ares/10852/ - 36

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10852/172.23.133.11.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10852/172.23.133.12.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10852/172.23.133.13.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-ares-10852/172.23.133.14.zip

Graphs:

http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=ares_650-4545_access_03e7&snapshot=ares_650-4546_access_7861