Index: xfs/include/linux/mm.h
===================================================================
--- xfs.orig/include/linux/mm.h	2012-09-21 17:50:32.243490371 +0200
+++ xfs/include/linux/mm.h	2012-09-21 17:50:43.333490305 +0200
@@ -1467,6 +1467,12 @@ void page_cache_async_readahead(struct a
 				pgoff_t offset,
 				unsigned long size);
 
+void page_cache_nonblock_readahead(struct address_space *mapping,
+				struct file_ra_state *ra,
+				struct file *filp,
+				pgoff_t offset,
+				unsigned long size);
+
 unsigned long max_sane_readahead(unsigned long nr);
 unsigned long ra_submit(struct file_ra_state *ra,
 			struct address_space *mapping,
Index: xfs/mm/filemap.c
===================================================================
--- xfs.orig/mm/filemap.c	2012-09-21 17:50:32.243490371 +0200
+++ xfs/mm/filemap.c	2012-09-21 18:35:53.343474115 +0200
@@ -1107,6 +1107,9 @@ static void do_generic_file_read(struct
 find_page:
 		page = find_get_page(mapping, index);
 		if (!page) {
+			if (filp && filp->f_flags & O_NONBLOCK)
+				goto short_read;
+
 			page_cache_sync_readahead(mapping,
 					ra, filp,
 					index, last_index - index);
@@ -1218,6 +1221,12 @@ page_not_up_to_date_locked:
 		}
 
 readpage:
+		if (filp && filp->f_flags & O_NONBLOCK) {
+			unlock_page(page);
+			page_cache_release(page);
+			goto short_read;
+		}
+
 		/*
 		 * A previous I/O error may have been due to temporary
 		 * failures, eg. multipath errors.
@@ -1293,6 +1302,10 @@ out:
 
 	*ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
 	file_accessed(filp);
+	return;
+short_read:
+	page_cache_nonblock_readahead(mapping, ra, filp, index,
+				      last_index - index);
 }
 
 int file_read_actor(read_descriptor_t *desc, struct page *page,
@@ -1466,7 +1479,8 @@ generic_file_aio_read(struct kiocb *iocb
 		do_generic_file_read(filp, ppos, &desc, file_read_actor);
 		retval += desc.written;
 		if (desc.error) {
-			retval = retval ?: desc.error;
+			if (!retval)
+				retval = desc.error;
 			break;
 		}
 		if (desc.count > 0)
Index: xfs/mm/readahead.c
===================================================================
--- xfs.orig/mm/readahead.c	2012-09-21 17:50:32.243490371 +0200
+++ xfs/mm/readahead.c	2012-09-21 17:50:43.336823641 +0200
@@ -565,6 +565,22 @@ page_cache_async_readahead(struct addres
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);
 
+void
+page_cache_nonblock_readahead(struct address_space *mapping,
+			   struct file_ra_state *ra, struct file *filp,
+			   pgoff_t offset, unsigned long req_size)
+{
+	/*
+	 * Defer asynchronous read-ahead on IO congestion.
+	 */
+	if (bdi_read_congested(mapping->backing_dev_info))
+		return;
+
+	/* do read-ahead */
+	ondemand_readahead(mapping, ra, filp, false, offset, req_size);
+}
+EXPORT_SYMBOL_GPL(page_cache_nonblock_readahead);
+
 static ssize_t
 do_readahead(struct address_space *mapping, struct file *filp,
 	     pgoff_t index, unsigned long nr)