MAX_STRUCT_PAGE_SIZE
unsigned long page_map_size = MAX_STRUCT_PAGE_SIZE * npfns;
if (sizeof(struct page) > MAX_STRUCT_PAGE_SIZE) {
if (sizeof(struct page) > MAX_STRUCT_PAGE_SIZE && page_struct_override)
pfn_sb->page_struct_size = cpu_to_le16(MAX_STRUCT_PAGE_SIZE);