gfs2: convert gfs2_getbuf() to folios

Remove several folio->page->folio conversions.  Also use __GFP_NOFAIL
instead of calling yield() and the new get_nth_bh().

Link: https://lkml.kernel.org/r/20231016201114.1928083-8-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Pankaj Raghav <p.raghav@samsung.com>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/gfs2/meta_io.c

@@ -115,7 +115,7 @@ struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
 {
 	struct address_space *mapping = gfs2_glock2aspace(gl);
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
-	struct page *page;
+	struct folio *folio;
 	struct buffer_head *bh;
 	unsigned int shift;
 	unsigned long index;
@@ -129,36 +129,31 @@ struct buffer_head *gfs2_getbuf(struct gfs2_glock *gl, u64 blkno, int create)
 	bufnum = blkno - (index << shift);  /* block buf index within page */
 
 	if (create) {
-		for (;;) {
-			page = grab_cache_page(mapping, index);
-			if (page)
-				break;
-			yield();
-		}
-		if (!page_has_buffers(page))
-			create_empty_buffers(page, sdp->sd_sb.sb_bsize, 0);
+		folio = __filemap_get_folio(mapping, index,
+				FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
+				mapping_gfp_mask(mapping) | __GFP_NOFAIL);
+		bh = folio_buffers(folio);
+		if (!bh)
+			bh = folio_create_empty_buffers(folio,
+				sdp->sd_sb.sb_bsize, 0);
 	} else {
-		page = find_get_page_flags(mapping, index,
-						FGP_LOCK|FGP_ACCESSED);
-		if (!page)
+		folio = __filemap_get_folio(mapping, index,
+				FGP_LOCK | FGP_ACCESSED, 0);
+		if (IS_ERR(folio))
 			return NULL;
-		if (!page_has_buffers(page)) {
-			bh = NULL;
-			goto out_unlock;
-		}
+		bh = folio_buffers(folio);
 	}
 
-	/* Locate header for our buffer within our page */
-	for (bh = page_buffers(page); bufnum--; bh = bh->b_this_page)
-		/* Do nothing */;
-	get_bh(bh);
+	if (!bh)
+		goto out_unlock;
 
+	bh = get_nth_bh(bh, bufnum);
 	if (!buffer_mapped(bh))
 		map_bh(bh, sdp->sd_vfs, blkno);
 
 out_unlock:
-	unlock_page(page);
-	put_page(page);
+	folio_unlock(folio);
+	folio_put(folio);
 
 	return bh;
 }