mm/hugetlb: use helper huge_page_order and pages_per_huge_page

Since commit a5516438 ("hugetlb: modular state for hugetlb page
size"), we can use huge_page_order to access hstate->order and
pages_per_huge_page to fetch the pages per huge page.  But
gather_bootmem_prealloc() forgot to use it.

Link: https://lkml.kernel.org/r/20210114114435.40075-1-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Reviewed-by: NMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -2476,7 +2476,7 @@ static void __init gather_bootmem_prealloc(void)
 		struct hstate *h = m->hstate;
 
 		WARN_ON(page_count(page) != 1);
-		prep_compound_huge_page(page, h->order);
+		prep_compound_huge_page(page, huge_page_order(h));
 		WARN_ON(PageReserved(page));
 		prep_new_huge_page(h, page, page_to_nid(page));
 		put_page(page); /* free it into the hugepage allocator */
@@ -2488,7 +2488,7 @@ static void __init gather_bootmem_prealloc(void)
 		 * side-effects, like CommitLimit going negative.
 		 */
 		if (hstate_is_gigantic(h))
-			adjust_managed_page_count(page, 1 << h->order);
+			adjust_managed_page_count(page, pages_per_huge_page(h));
 		cond_resched();
 	}
 }