mm: convert split_huge_pages_pid() to use a folio

Replaces five calls to compound_head with one.

Link: https://lkml.kernel.org/r/20230816151201.3655946-14-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/huge_memory.c

@@ -584,14 +584,11 @@ void folio_prep_large_rmappable(struct folio *folio)
 	folio_set_large_rmappable(folio);
 }
 
-static inline bool is_transparent_hugepage(struct page *page)
+static inline bool is_transparent_hugepage(struct folio *folio)
 {
-	struct folio *folio;
-
-	if (!PageCompound(page))
+	if (!folio_test_large(folio))
 		return false;
 
-	folio = page_folio(page);
 	return is_huge_zero_page(&folio->page) ||
 		folio_test_large_rmappable(folio);
 }
@@ -3012,6 +3009,7 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 	for (addr = vaddr_start; addr < vaddr_end; addr += PAGE_SIZE) {
 		struct vm_area_struct *vma = vma_lookup(mm, addr);
 		struct page *page;
+		struct folio *folio;
 
 		if (!vma)
 			break;
@@ -3028,22 +3026,23 @@ static int split_huge_pages_pid(int pid, unsigned long vaddr_start,
 		if (IS_ERR_OR_NULL(page))
 			continue;
 
-		if (!is_transparent_hugepage(page))
+		folio = page_folio(page);
+		if (!is_transparent_hugepage(folio))
 			goto next;
 
 		total++;
-		if (!can_split_folio(page_folio(page), NULL))
+		if (!can_split_folio(folio, NULL))
 			goto next;
 
-		if (!trylock_page(page))
+		if (!folio_trylock(folio))
 			goto next;
 
-		if (!split_huge_page(page))
+		if (!split_folio(folio))
 			split++;
 
-		unlock_page(page);
+		folio_unlock(folio);
 next:
-		put_page(page);
+		folio_put(folio);
 		cond_resched();
 	}
 	mmap_read_unlock(mm);