Looks like the default allocator uses mmap(2) for every single allocation, which is horribly inefficient - you map a whole PAGE_SIZE worth of memory for every tiny string. Aside from just wasting memory this will make the TLB very unhappy.

It looks like sp_log's string formatting is entirely unbuffered which results in lots of tiny write syscalls.

Thanks for reading. "There is no heap" is meant to say that your mental model of memory shouldn't be one heap from which all memory is pulled. It should be many heaps, owned by many different allocators and providing different semantics. Hence the opinionated stance of the library; there is no allocation function that does not force you to specify the specific heap you want to allocate from. I'm sorry if I didn't explain that well.

As far as the syscall thing, it's actually quite interesting. NT is also extremely stable. Likewise for the stock Darwin syscalls on macOS. In practice, though, Windows loads kernel32.dll automatically, so there's no drawback in using it when appropriate. I still call directly into NT sometimes (mostly to skip complex userspace path translations that aren't useful). On macOS, you are likewise forced to link to libc (libSystem.dylib), and so I usually just end up using the syscall-wrapper libc functions there.

> Works nicely on Linux where the syscall interface is explicitly stable, but on many (most?) other platforms this is not the case.

There is a footnote on this saying as much:

> 3. Where “syscall” means “the lowest level primitive available”. On Linux, it’s always actual syscalls. On Windows, that’s usually NT. On macOS, it’s usually the syscall-wrapper subset of libc because you’re forced to link libc and it’s not quite as open as Linux (although there is a rich “undocumented” set of APIs and syscalls that are very interesting).

The "definition of a heap allocation interface" indicates that there is no standard heap. Instead, there's a standard interface for the use to define their own heaps. Any standard library function that needs to allocate will take a sp_allocator_t parameter, and use that to allocate. As opposed to e.g. strdup, which hard-codes a call to malloc internally. Sp.h's strdup-alike would take an sp_allocator_t as input and call into that to get the memory it needs.

A C++ programmer might describe this as "PMR, but not default-constructible. And std::stable_sort takes a PMR allocator parameter. And PMR is the default, and there's no implementation of std::allocator (or new or delete)."