An OS kernel has no business maintaining, and even less business accessing in bulk, large data structures that are performance-critical enough to worry about coherent memory access. It is also an infrastructure-deprived environment in which swapping around pointers to implement a linked list with correct locking is relatively easy to get right but allocating vectors is out of the question.

> An OS kernel has no business maintaining, and even less business accessing in bulk, large data structures that are performance-critical enough to worry about coherent memory access

File systems are usually part of the kernel.

File systems tend not to have large data structures. They are relatively modest data structures which manage bulk access to large blocks of data. A subtle distinction, but important in this context.

Really? Even huge volumes with loads of tiny files? Mail and Usenet servers? Build servers? What is your definition of large and modest here?

The data structures under discussion here are those used to track individual files. Yes, there can be squillions of them, but as data structures, they are, in fact, rather modest.