I noticed while analysing some data from a YCSB run that the reported cache: maximum page size at eviction (MB) of 928MB, which is far above the expected value.

The YCSB 6.0 configuration is:

fieldcount=10
fieldlength=10
recordcount=120000000
operationcount=100000000
workload=com.yahoo.ycsb.workloads.CoreWorkload
readallfields=true
readproportion=0.5
updateproportion=0.5
scanproportion=0
insertproportion=0

The original test was run on a machine with 256GB of memory, and a 3 disk SSD raid 0 array.

MongoDB was started with the journal on a separate drive and the following options:

mongod --wiredTigerEngineConfigString="eviction_dirty_trigger=95,eviction_dirty_target=80"