netfs: Fault in smaller chunks for non-large folio mappings

As in commit 4e527d58 ("iomap: fault in smaller chunks for non-large
folio mappings"), we can see a performance loss for filesystems
which have not yet been converted to large folios.

Fixes: c38f4e96 ("netfs: Provide func to copy data to pagecache for buffered write")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240527201735.1898381-1-willy@infradead.orgReviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/netfs/buffered_write.c

@@ -184,7 +184,7 @@ ssize_t netfs_perform_write(struct kiocb *iocb, struct iov_iter *iter,
 	unsigned int bdp_flags = (iocb->ki_flags & IOCB_NOWAIT) ? BDP_ASYNC : 0;
 	ssize_t written = 0, ret, ret2;
 	loff_t i_size, pos = iocb->ki_pos, from, to;
-	size_t max_chunk = PAGE_SIZE << MAX_PAGECACHE_ORDER;
+	size_t max_chunk = mapping_max_folio_size(mapping);
 	bool maybe_trouble = false;
 
 	if (unlikely(test_bit(NETFS_ICTX_WRITETHROUGH, &ctx->flags) ||