[PATCH v3 21/21] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page

[Muchun Song]

There are only `RESERVE_VMEMMAP_SIZE / sizeof(struct page)` struct pages
can be used when CONFIG_HUGETLB_PAGE_FREE_VMEMMAP, so add a BUILD_BUG_ON
to catch this invalid usage of tail struct page.

Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/hugetlb.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1dd1a9cec008..66b96705597a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3946,6 +3946,8 @@ static int __init hugetlb_init(void)
 
 #ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
 	BUILD_BUG_ON_NOT_POWER_OF_2(sizeof(struct page));
+	BUILD_BUG_ON(NR_USED_SUBPAGE >=
+		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
 #endif
 
 	if (!hugepages_supported()) {
-- 
2.11.0