diff options
| -rw-r--r-- | include/linux/mm_types.h | 5 | ||||
| -rw-r--r-- | include/linux/page-flags.h | 25 |
2 files changed, 20 insertions, 10 deletions
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 278eade2ad4c..ef09c4eef6d3 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -157,6 +157,11 @@ struct page { * * See page-flags.h for a list of page types which are currently * stored here. + * + * Owners of typed folios may reuse the lower 16 bit of the + * head page page_type field after setting the page type, + * but must reset these 16 bit to -1 before clearing the + * page type. */ unsigned int page_type; diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index b041bc058fb1..d221a6a14764 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -941,16 +941,21 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpoisoned) */ enum pagetype { - PG_buddy = 0x00000080, - PG_offline = 0x00000100, - PG_table = 0x00000200, - PG_guard = 0x00000400, - PG_hugetlb = 0x00000800, - PG_slab = 0x00001000, - - PAGE_TYPE_BASE = 0xf0000000, - /* Reserve 0x0000007f to catch underflows of _mapcount */ - PAGE_MAPCOUNT_RESERVE = -128, + PG_buddy = 0x40000000, + PG_offline = 0x20000000, + PG_table = 0x10000000, + PG_guard = 0x08000000, + PG_hugetlb = 0x04000000, + PG_slab = 0x02000000, + + PAGE_TYPE_BASE = 0x80000000, + + /* + * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflows and + * allow owners that set a type to reuse the lower 16 bit for their own + * purposes. + */ + PAGE_MAPCOUNT_RESERVE = ~0x0000ffff, }; #define PageType(page, flag) \ |