As Thadeu Lima de Souza Cascardo said, the build time detected page size isn't correct, perhaps using --with-lg-page=/--with-lg-page-sizes at compile time.
This is available in the 3.6.0 version of jemalloc. (upstream currently at 4.4.0). As an aside, I've got part way though an upstream patch to change this to runtime detection, no idea when it will be complete, and I have been told that upstream won't risk performance regressions.
