hugetlb_cgroup: use helper pages_per_huge_page() in hugetlb_cgroup

We could use helper function pages_per_huge_page() to get the number of
pages in a hstate to simplify the code slightly.

Link: https://lkml.kernel.org/r/20210205084513.29624-1-linmiaohe@huawei.comSigned-off-by: NMiaohe Lin <linmiaohe@huawei.com>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb_cgroup.c

@@ -113,7 +113,7 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,
 			rsvd_parent);
 
 		limit = round_down(PAGE_COUNTER_MAX,
-				   1 << huge_page_order(&hstates[idx]));
+				   pages_per_huge_page(&hstates[idx]));
 
 		ret = page_counter_set_max(
 			hugetlb_cgroup_counter_from_cgroup(h_cgroup, idx),
@@ -460,7 +460,7 @@ static int hugetlb_cgroup_read_u64_max(struct seq_file *seq, void *v)
 	counter = &h_cg->hugepage[idx];
 
 	limit = round_down(PAGE_COUNTER_MAX,
-			   1 << huge_page_order(&hstates[idx]));
+			   pages_per_huge_page(&hstates[idx]));
 
 	switch (MEMFILE_ATTR(cft->private)) {
 	case RES_RSVD_USAGE:
@@ -507,7 +507,7 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
 		return ret;
 
 	idx = MEMFILE_IDX(of_cft(of)->private);
-	nr_pages = round_down(nr_pages, 1 << huge_page_order(&hstates[idx]));
+	nr_pages = round_down(nr_pages, pages_per_huge_page(&hstates[idx]));
 
 	switch (MEMFILE_ATTR(of_cft(of)->private)) {
 	case RES_RSVD_LIMIT: