On Mon, Dec 20, 2021 at 09:03:12PM -0400, Jason Gunthorpe wrote: > That just leave the THP splitting.. I suppose we get the PTL, then > compute the current value of the new bit based on refcount and diffuse > it to all tail pages, then update the PMD and release the PTL. Safe > against concurrent WP - don't need DoubleMap horrors because it isn't > a counter. One of the things I've been trying to figure out is how we do can_split_huge_page(). Maybe an rmap walk to figure out how many refcounts we would subtract if we did unmap it from everywhere it's currently mapped? (just to be clear, we call unmap_page() as the next thing, so I don't mind warming up the rbtree cachelines if it's mapped anywhere)
