[PATCH v6 16/16] 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 <songmuc...@bytedance.com>
---
 mm/hugetlb_vmemmap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index b2222f8d1245..d2c013582110 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -338,6 +338,9 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
        unsigned int order = huge_page_order(h);
        unsigned int vmemmap_pages;
 
+       BUILD_BUG_ON(NR_USED_SUBPAGE >=
+                    RESERVE_VMEMMAP_SIZE / sizeof(struct page));
+
        if (!is_power_of_2(sizeof(struct page)) ||
            !hugetlb_free_vmemmap_enabled) {
                pr_info("disable freeing vmemmap pages for %s\n", h->name);
-- 
2.11.0