21 Dec
2021
21 Dec
'21
3:29 a.m.
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)