mm/shmem: convert shmem_alloc_and_acct_page to use a folio

Convert shmem_alloc_hugepage() to return the folio that it uses and use a
folio throughout shmem_alloc_and_acct_page().  Continue to return a page
from shmem_alloc_and_acct_page() for now.

Link: https://lkml.kernel.org/r/20220504182857.4013401-22-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/shmem.c

@@ -1523,7 +1523,7 @@ static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
 	return result;
 }
 
-static struct page *shmem_alloc_hugepage(gfp_t gfp,
+static struct folio *shmem_alloc_hugefolio(gfp_t gfp,
 		struct shmem_inode_info *info, pgoff_t index)
 {
 	struct vm_area_struct pvma;
@@ -1541,7 +1541,7 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
 	shmem_pseudo_vma_destroy(&pvma);
 	if (!folio)
 		count_vm_event(THP_FILE_FALLBACK);
-	return &folio->page;
+	return folio;
 }
 
 static struct folio *shmem_alloc_folio(gfp_t gfp,
@@ -1568,7 +1568,7 @@ static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
 		pgoff_t index, bool huge)
 {
 	struct shmem_inode_info *info = SHMEM_I(inode);
-	struct page *page;
+	struct folio *folio;
 	int nr;
 	int err = -ENOSPC;
 
@@ -1580,13 +1580,13 @@ static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
 		goto failed;
 
 	if (huge)
-		page = shmem_alloc_hugepage(gfp, info, index);
+		folio = shmem_alloc_hugefolio(gfp, info, index);
 	else
-		page = shmem_alloc_page(gfp, info, index);
-	if (page) {
-		__SetPageLocked(page);
-		__SetPageSwapBacked(page);
-		return page;
+		folio = shmem_alloc_folio(gfp, info, index);
+	if (folio) {
+		__folio_set_locked(folio);
+		__folio_set_swapbacked(folio);
+		return &folio->page;
 	}
 
 	err = -ENOMEM;