mm/shmem: add shmem_alloc_folio()

Call vma_alloc_folio() directly instead of alloc_page_vma().  Add a
shmem_alloc_page() wrapper to avoid changing the callers.

Link: https://lkml.kernel.org/r/20220504182857.4013401-21-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

@@ -1544,17 +1544,23 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
 	return &folio->page;
 }
 
-static struct page *shmem_alloc_page(gfp_t gfp,
+static struct folio *shmem_alloc_folio(gfp_t gfp,
 			struct shmem_inode_info *info, pgoff_t index)
 {
 	struct vm_area_struct pvma;
-	struct page *page;
+	struct folio *folio;
 
 	shmem_pseudo_vma_init(&pvma, info, index);
-	page = alloc_page_vma(gfp, &pvma, 0);
+	folio = vma_alloc_folio(gfp, 0, &pvma, 0, false);
 	shmem_pseudo_vma_destroy(&pvma);
 
-	return page;
+	return folio;
+}
+
+static struct page *shmem_alloc_page(gfp_t gfp,
+			struct shmem_inode_info *info, pgoff_t index)
+{
+	return &shmem_alloc_folio(gfp, info, index)->page;
 }
 
 static struct page *shmem_alloc_and_acct_page(gfp_t gfp,