mm/mempolicy: use a folio in do_mbind()

We actually add folios to the pagelist already, but then work with them as
pages.  Removes a call to compound_head() in PageKsm() and removes a
reference to page->index.

Link: https://lkml.kernel.org/r/20240229153015.1996829-1-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Gregory Price <gregory.price@memverge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/mempolicy.c

@@ -1356,29 +1356,30 @@ static long do_mbind(unsigned long start, unsigned long len,
 		 */
 		if (new->mode == MPOL_INTERLEAVE ||
 		    new->mode == MPOL_WEIGHTED_INTERLEAVE) {
-			struct page *page;
+			struct folio *folio;
 			unsigned int order;
 			unsigned long addr = -EFAULT;
 
-			list_for_each_entry(page, &pagelist, lru) {
-				if (!PageKsm(page))
+			list_for_each_entry(folio, &pagelist, lru) {
+				if (!folio_test_ksm(folio))
 					break;
 			}
-			if (!list_entry_is_head(page, &pagelist, lru)) {
+			if (!list_entry_is_head(folio, &pagelist, lru)) {
 				vma_iter_init(&vmi, mm, start);
 				for_each_vma_range(vmi, vma, end) {
-					addr = page_address_in_vma(page, vma);
+					addr = page_address_in_vma(
+						folio_page(folio, 0), vma);
 					if (addr != -EFAULT)
 						break;
 				}
 			}
 			if (addr != -EFAULT) {
-				order = compound_order(page);
+				order = folio_order(folio);
 				/* We already know the pol, but not the ilx */
 				mpol_cond_put(get_vma_policy(vma, addr, order,
 							     &mmpol.ilx));
 				/* Set base from which to increment by index */
-				mmpol.ilx -= page->index >> order;
+				mmpol.ilx -= folio->index >> order;
 			}
 		}
 	}