Document hugetlb's use of a zero compound order so support for zero
orders is not removed from folio_set_compound_order().
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Suggested-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Suggested-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
This can be folded into f2b67a51d0ef6871d4fb0c3e8199f278112bd108
mm: add folio dtor and order setter functions
include/linux/mm.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 443d496949a8..cd8508d728f1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -999,9 +999,16 @@ static inline void set_compound_order(struct page *page, unsigned int order)
#endif
}
+/*
+ * folio_set_compound_order is generally passed a non-zero order to
+ * initialize a large folio. However, hugetlb code abuses this by
+ * passing in zero when 'dissolving' a large folio.
+ */
static inline void folio_set_compound_order(struct folio *folio,
unsigned int order)
{
+ VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
+
folio->_folio_order = order;
#ifdef CONFIG_64BIT
folio->_folio_nr_pages = order ? 1U << order : 0;
--
2.38.1
