In incremental build of indexing perf test with MOI, indexer_rss goes high for some time and drops

Observed that in incremental build of indexes, indexer_rss grows high for around 300sec and then drops, then remains almost stable.
Here are jobs, logs can be found in job's console output:
100M:
cbmonitor URL- http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=nyx_500-2110_build_incrindex_4e14
Job- http://perf.jenkins.couchbase.com/job/secondary-moi/1462/
1B:
cbmonitor URL- http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=nyx_500-2110_build_incrindex_7cf1
Job- http://perf.jenkins.couchbase.com/job/secondary-moi/1464/

Note that similar behaviour observed in 4.5.1 and 4.6.0