Depends on how things are approached.
You could, for example, take advantage of bump arena allocator in rust which would allow the linker to have just 1 alloc/dealloc. Mold is still using more traditional allocators under the covers which won't be as fast as a bump allocator. (Nothing would stop mold from doing the same).
Traditional allocators are fast if you never introduce much fragmentation with free, though you may still get some gaps and have some other overhead and not be quite as fast. But why couldn't you just LD_PRELOAD a malloc for mold that worked as a bump/stack/arena allocator and just ignored free if anything party stuff isn't making that many allocations?
> Traditional allocators are fast
Really it's allocators in general. Allocations are perceived as expensive only because they are mostly dependent on the amortized cost of prior deallocations. As an extreme example, even GCs can be fast if you avoid deallocation because most typically have a long-lived object heap that rarely gets collected - so if you keep things around that can be long-lived (pooling) their cost mostly goes away.
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