mm/swap: fix release_pages() when releasing devmap pages

release_pages() is an optimized version of a loop around put_page().
Unfortunately for devmap pages the logic is not entirely correct in
release_pages().  This is because device pages can be more than type
MEMORY_DEVICE_PUBLIC.  There are in fact 4 types, private, public, FS DAX,
and PCI P2PDMA.  Some of these have specific needs to "put" the page while
others do not.

This logic to handle any special needs is contained in
put_devmap_managed_page().  Therefore all devmap pages should be processed
by this function where we can contain the correct logic for a page put.

Handle all device type pages within release_pages() by calling
put_devmap_managed_page() on all devmap pages.  If
put_devmap_managed_page() returns true the page has been put and we
continue with the next page.  A false return of put_devmap_managed_page()
means the page did not require special processing and should fall to
"normal" processing.

This was found via code inspection while determining if release_pages()
and the new put_user_pages() could be interchangeable.[1]

[1] https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Cc: Jérôme Glisse <[email protected]>
Cc: Michal Hocko <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Reviewed-by: John Hubbard <[email protected]>
Signed-off-by: Ira Weiny <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>

mm/swap.c

@@ -740,15 +740,20 @@ void release_pages(struct page **pages, int nr)
 		if (is_huge_zero_page(page))
 			continue;
 
-		/* Device public page can not be huge page */
-		if (is_device_public_page(page)) {
+		if (is_zone_device_page(page)) {
 			if (locked_pgdat) {
 				spin_unlock_irqrestore(&locked_pgdat->lru_lock,
 						       flags);
 				locked_pgdat = NULL;
 			}
-			put_devmap_managed_page(page);
-			continue;
+			/*
+			 * ZONE_DEVICE pages that return 'false' from
+			 * put_devmap_managed_page() do not require special
+			 * processing, and instead, expect a call to
+			 * put_page_testzero().
+			 */
+			if (put_devmap_managed_page(page))
+				continue;
 		}
 
 		page = compound_head(page);