Memory management generally works at the level of pages, which typically
contain 4,096 bytes but may be larger. The kernel, though, has extended
the concept of pages to include compound pages, which are groups of
contiguous single pages. That, in turn, has made the definition of
what a “page” is a bit fuzzy. Matthew Wilcox has been working since last
year on a concept called “page folios” which is meant to bring the picture
back into focus; whether the memory-management community will accept it
remains unclear, though.

Source: LWN.net – [$] Clarifying memory management with page folios