With the changes in Durable History we have noticed that the MongoDB memory allocation overhead in tcmalloc is higher by up to 20%. The wiredtiger_open API call has a cache_overhead configuration setting that aims to account for that overhead.

We should consider increasing the default value for the cache_overhead setting from 8 to something higher (I'd suggest trying 15) in order to avoid operational issues for users who might run into out of memory (OOM) issues in their production environments due to increased fragmentation.