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In this test jemalloc actually uses the most memory of all. With default tunings it uses 700k pages at peak, compared to 170k for tcmalloc and 131k for glibc. I have no idea if that is relevant in real life and I have never cared, so I didn't mention it.

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That's due to differences in your workload - in e.g. Ruby on Rails, the total uncertainty of which objects are going to survive a request means that jemalloc does a much better job at packing.

That's actually quite interesting, as IIRC jemalloc has much looser alignment than other allocators and thus can give "tighter" blocks for small allocations.

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