mm/hugetlb-cgroup: convert hugetlb_cgroup_css_offline() to work on folios

Let's convert hugetlb_cgroup_css_offline() and
hugetlb_cgroup_move_parent() to work on folios.  hugepage_activelist
contains folios, not pages.

While at it, rename page_hcg simply to hcg, removing most of the "page"
terminology.

This removes an unnecessary call to compound_head().

Link: https://lkml.kernel.org/r/20250113131611.2554758-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: davidhildenbrand

mm/hugetlb_cgroup.c

@@ -195,24 +195,23 @@ static void hugetlb_cgroup_css_free(struct cgroup_subsys_state *css)
  * cannot fail.
  */
 static void hugetlb_cgroup_move_parent(int idx, struct hugetlb_cgroup *h_cg,
-				       struct page *page)
+				       struct folio *folio)
 {
 	unsigned int nr_pages;
 	struct page_counter *counter;
-	struct hugetlb_cgroup *page_hcg;
+	struct hugetlb_cgroup *hcg;
 	struct hugetlb_cgroup *parent = parent_hugetlb_cgroup(h_cg);
-	struct folio *folio = page_folio(page);
 
-	page_hcg = hugetlb_cgroup_from_folio(folio);
+	hcg = hugetlb_cgroup_from_folio(folio);
 	/*
 	 * We can have pages in active list without any cgroup
 	 * ie, hugepage with less than 3 pages. We can safely
 	 * ignore those pages.
 	 */
-	if (!page_hcg || page_hcg != h_cg)
+	if (!hcg || hcg != h_cg)
 		goto out;
 
-	nr_pages = compound_nr(page);
+	nr_pages = folio_nr_pages(folio);
 	if (!parent) {
 		parent = root_h_cgroup;
 		/* root has no limit */
@@ -235,13 +234,13 @@ static void hugetlb_cgroup_css_offline(struct cgroup_subsys_state *css)
 {
 	struct hugetlb_cgroup *h_cg = hugetlb_cgroup_from_css(css);
 	struct hstate *h;
-	struct page *page;
+	struct folio *folio;
 
 	do {
 		for_each_hstate(h) {
 			spin_lock_irq(&hugetlb_lock);
-			list_for_each_entry(page, &h->hugepage_activelist, lru)
-				hugetlb_cgroup_move_parent(hstate_index(h), h_cg, page);
+			list_for_each_entry(folio, &h->hugepage_activelist, lru)
+				hugetlb_cgroup_move_parent(hstate_index(h), h_cg, folio);
 
 			spin_unlock_irq(&hugetlb_lock);
 		}