From what I can tell, that code is in a conditional which checks whether the new processes can fit in main memory. If it can fit, it jumps to line 1913.
Anyhow, there's a difference between the fork interface being a hack, and the fork implementation being a hack. Unix is is a cornucopia of implementation hacks. That doesn't mean the interfaces weren't deliberately and thoughtfully designed.
Much like C, what makes Unix unique and still relevant is that the deliberate design took into account practical implementation considerations. Unix and C are most elegant from an engineer's perspective. It's an interesting balance of interface complexity and implementation complexity. This is why some people claim that the Unix design philosophy epitomizes "worse is better".
Anyhow, there's a difference between the fork interface being a hack, and the fork implementation being a hack. Unix is is a cornucopia of implementation hacks. That doesn't mean the interfaces weren't deliberately and thoughtfully designed.
Much like C, what makes Unix unique and still relevant is that the deliberate design took into account practical implementation considerations. Unix and C are most elegant from an engineer's perspective. It's an interesting balance of interface complexity and implementation complexity. This is why some people claim that the Unix design philosophy epitomizes "worse is better".