We had a production system that has been working fine slow to a crawl and kick users out after the memory usage grew to 99% overall. 

We are currently on 3.6.10 

Single server, no replica set

Config has wiredTiger.cacheSizeGB: 13

Total system memory is 24gb

values reported by mongostat were

vsize  40gb

res was 19

dirty .8%

used 80%

I have the metrics files from the diagnostic.data for the time frame, are there tools available yet so I can analyze these?