WiredTiger cache size is only configurable in whole gigabytes.

Hello, on our development servers we currently run our application server alongside a standalone mongod instance. Ever since WiredTiger was introduced we have the occasional OOM killer issue where app server RAM + WT cache + file system buffers are way higher than these smaller instances have.

I was looking into overriding the WT cache size into something smaller and found this option:
https://docs.mongodb.org/manual/reference/configuration-options/#storage.wiredTiger.engineConfig.cacheSizeGB

The problem is that this only allows this value to be specified in whole gigabytes while total RAM of these instances is only 1 or 2 Gb. Specifying this value as a fraction results in parse errors as this field is parsed as an integer. I also tried other key names such as 'cacheSizeMB' or 'cacheSize' without any luck. I also tried using a letter as in indicator ('200M') but that leads to another parsing error.

I found a workaround in this post but that does not seem to work (anymore?):
https://groups.google.com/forum/#!topic/mongodb-user/GLrp-H31YWg

Are there plans to specify this value in a more specific way. Also, is there a current workaround for this?