The space IS allocated, it's just that this space (virtual memory) is not backed by physical RAM.
Try telling that to the C standard. It has no notion of virtual or physical memory. If it's allocated that means you can read/write to it, end of story.
> It has no notion of virtual or physical memory.
Exactly! That's why once virtual memory is allocated, malloc() is allowed to consider the operation successful. The standard does not care at all whether it is virtual memory allocation or physical memory allocation. It is completely unspecified in the standard what sort of memory must be allocated. So no spec in the standard is being violated by returning non-null pointer for virtual memory allocation.
> The pointer returned if the allocation succeeds is suitably aligned so that [...]
> If the space cannot be allocated, a null pointer is returned.
If you use mmap and "from your perspective" that's considered success then it's your perspective that's faulty. The standard is literally telling you right here^ there are 2 possibilities: either you allocate the space and return a pointer to the space, or you don't and you return null. There is no third option of "space cannot be allocated but you return non-null anyway". That's quite literally the end of the story.