There was a mention somewhere that rustc (the compiler itself) still uses jemalloc, glibc 2.24(?) was about 10% slower. Compilers tend to use a lot of small allocations, so most code probably is less affected than that.

I think the big selling point of jemalloc when it appeared was that it was much better for multithreaded applications. But since then glibc has improved a lot in this area, and nowadays has a similiar design with per-thread pools etc.