netfs: Allocate multipage folios in the writepath

Allocate a multipage folio when copying data into the pagecache if possible
if there's sufficient data to warrant it.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org

fs/netfs/buffered_write.c

@@ -84,14 +84,19 @@ static enum netfs_how_to_modify netfs_how_to_modify(struct netfs_inode *ctx,
 }
 
 /*
- * Grab a folio for writing and lock it.
+ * Grab a folio for writing and lock it.  Attempt to allocate as large a folio
+ * as possible to hold as much of the remaining length as possible in one go.
  */
 static struct folio *netfs_grab_folio_for_write(struct address_space *mapping,
 						loff_t pos, size_t part)
 {
 	pgoff_t index = pos / PAGE_SIZE;
+	fgf_t fgp_flags = FGP_WRITEBEGIN;
 
-	return __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
+	if (mapping_large_folio_support(mapping))
+		fgp_flags |= fgf_set_order(pos % PAGE_SIZE + part);
+
+	return __filemap_get_folio(mapping, index, fgp_flags,
 				   mapping_gfp_mask(mapping));
 }