Hello,

this is the latest version of the mremap THP native implementation
plus optimizations.

So first question is: am I right, the "- 1" that I am removing below
was buggy? It's harmless because these old_end/next are page aligned,
but if PAGE_SIZE would be 1, it'd break, right? It's really confusing
to read even if it happens to work. Please let me know because that "-
1" ironically it's the thing I'm less comfortable about in this patch.

diff --git a/mm/mremap.c b/mm/mremap.c

--- a/mm/mremap.c
+++ b/mm/mremap.c

@@ -134,14 +126,17 @@ unsigned long move_page_tables(struct vm
 	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 		cond_resched();
 		next = (old_addr + PMD_SIZE) & PMD_MASK;
-		if (next - 1 > old_end)
+		if (next > old_end)
 			next = old_end;
 		extent = next - old_addr;
 		old_pmd = get_old_pmd(vma->vm_mm, old_addr);