The main problem with this approach for us is not throughput, MALLOC_ARENA_MAX is a maximum number of arenas per core, and our new servers have 48 cores, meaning we would still have a huge number of arenas and fragmentation problem. Yes, it will be a bit better but not even close to tcmalloc.
There is a good post by Heroku with some tests of different MALLOC_ARENA_MAX, that can give more insight on performance hit. https://devcenter.heroku.com/articles/testing-cedar-14-memor...
