Matthew Wilcox has worked hard on a patch series originally called “folios” that aims to “allow filesystems and the page cache to manage memory in larger chunks than PAGE_SIZE. Modern microprocessors use a unit of memory management known as a “page” that’s typically around 4KB in size. This is the smallest size of memory that can be tracked by a Memory Management Unit, and is also the fundamental size handled by the low-level (page) memory allocator in Linux.
The trouble is that 4KB isn’t all that large these days. In fact, if Linux needs to track all memory in units of 4K then the overhead becomes significant. Instead of doing this, there are times when groups of related pages can be managed as a chunk, or “folio” in the original patches. Linus preferred a much more boring name such as “pageset”. The choice of (re)name alone is not likely to get the patches accepted into 5.15, however, in spite of developers calling for clarity, due to ongoing debate about the best approach.