memcg: use a folio in get_mctgt_type_thp

Replace five calls to compound_head() with one.

Link: https://lkml.kernel.org/r/20240111181219.3462852-5-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memcontrol.c

@@ -6194,6 +6194,7 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
 		unsigned long addr, pmd_t pmd, union mc_target *target)
 {
 	struct page *page = NULL;
+	struct folio *folio;
 	enum mc_target_type ret = MC_TARGET_NONE;
 
 	if (unlikely(is_swap_pmd(pmd))) {
@@ -6203,17 +6204,18 @@ static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
 	}
 	page = pmd_page(pmd);
 	VM_BUG_ON_PAGE(!page || !PageHead(page), page);
+	folio = page_folio(page);
 	if (!(mc.flags & MOVE_ANON))
 		return ret;
-	if (page_memcg(page) == mc.from) {
+	if (folio_memcg(folio) == mc.from) {
 		ret = MC_TARGET_PAGE;
 		if (target) {
-			get_page(page);
-			if (!trylock_page(page)) {
-				put_page(page);
+			folio_get(folio);
+			if (!folio_trylock(folio)) {
+				folio_put(folio);
 				return MC_TARGET_NONE;
 			}
-			target->folio = page_folio(page);
+			target->folio = folio;
 		}
 	}
 	return ret;