mallctl_f("opt.lg_chunk", ...) is failing in memory init with jemalloc 5.1.0. It seems this was removed in 5.0.0 https://github.com/jemalloc/jemalloc/releases/tag/5.0.0 and 5.0 no longer operates with the concept of lg_chunk :
There is no equivalent replacement functionality.
For this specific issue, lg_chunk is used by PerconaFT to set the threshold where allocations will switch to using mmap instead of the standard allocator. It is reasonable to recognize the lg_chunk query failure and pick a rational value and continue on rather than failing and asserting. For the older jemalloc, this value was 4MB by default. We should use 4MB in the case that the lg_chunk query fails.