VSZ(gb) RSS(gb) malloc
7.9 4.8 jemalloc-3.6.0
13.6 12.4 glibc-2.23
I am not sure that it is possible to use a large RocksDB block cache with glibc malloc, where large means that it gets about 80% of RAM.
I previously shared results for MySQL and for MongoDB. There have been improvements over the past few years to make glibc malloc perform better on many-core servers. I don't know whether that work also made it better at avoiding fragmentation.