mm/page_alloc: let page freeing clear any set page type

Currently, any user of page types must clear that type before freeing a
page back to the buddy, otherwise we'll run into mapcount related sanity
checks (because the page type currently overlays the page mapcount).

Let's allow for not clearing the page type by page type users by letting
the buddy handle it instead.

We'll focus on having a page type set on the first page of a larger
allocation only.

With this change, we can reliably identify typed folios even though they
might be in the process of getting freed, which will come in handy in
migration code (at least in the transition phase).

In the future we might want to warn on some page types.  Instead of having
an "allow list", let's rather wait until we know about once that should go
on such a "disallow list".

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Acked-by: Harry Yoo <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Brendan Jackman <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Chengming Zhou <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Eugenio Pé rez <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Jerrin Shaji George <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Madhavan Srinivasan <[email protected]>
Cc: Mathew Brost <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Qi Zheng <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xuan Zhuo <[email protected]>
Cc: xu xin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4f55f8ed65c7..6318c85d678e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1380,6 +1380,10 @@ __always_inline bool free_pages_prepare(struct page *page,
 			mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
 		page->mapping = NULL;
 	}
+	if (unlikely(page_has_type(page)))
+		/* Reset the page_type (which overlays _mapcount) */
+		page->page_type = UINT_MAX;
+
 	if (is_check_pages_enabled()) {
 		if (free_page_is_bad(page))
 			bad++;