The filesystem doesn't just read from one part of the disk and write to another part of the disk, it reads from the disk and stores the result in memory, or it

The filesystem doesn't just read from one part of the disk and write to another part of the disk, it reads from the disk and stores the result in memory, or it takes data from memory and writes it to the disk. The other part of the kernel that deals with data in memory is the cache. Rather than have two separate representations of "data in memory" and have to translate between them all the time, it makes sense to have one representation of "data in memory" that all the affected systems can use to talk to each other. Even though the kernel now has multiple representations of "data in memory" due to advances in other parts of the kernel, it's still desirable to have just one representation shared between the cache and the filesystem, which is why people are talking about removing the old ones, and porting old code to use the new ones.