[PATCH v4 20/21] mm/hugetlb: Add BUILD_BUG_ON to catch invalid usage of tail struct page

[Muchun Song <songmuchun@xxxxxxxxxxxxx>]

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_vmemmap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 5c00826a98b3..f67aec6e3bb1 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -717,6 +717,9 @@ static int __init vmemmap_ptlock_init(void)
 {
 	int nid;
 
+	BUILD_BUG_ON(NR_USED_SUBPAGE >=
+		     RESERVE_VMEMMAP_SIZE / sizeof(struct page));
+
 	if (!hugepages_supported())
 		return 0;
 
-- 
2.11.0