The Transparent Huge Pages(THP) support in recent Linux kernels allows automatic promotion/demotion between different page sizes (e.g., 4KB and 2MB in x86-64).
But I am not sure if THP can also promote/demote page sizes between 4KB and 1GB pages or between 2MB and 1GB pages.
Can somebody comment on this?
According to this article
http://lwn.net/Articles/423584/
So, it seems that THP support implemented for 4k -> 2M/4M merging/splitting.
Also, in kernel sources I've seen that there is a split_huge_page_pmd function and as
PMD
undergoes to splitting andPMD
manages page entries on top ofPTE's
that has a fixed 4k size I supposed thatPMD
size (2M/4M) is the maximum transparent huge page size.