[PATCH] Fix mpage_readpage() for big requests

The problem is, if we increase our readhead size arbitrarily (say 2M), we
call mpage_readpages() with 2M and when it tries to allocated a bio enough to
fit 2M it fails, then we kick it back to "confused" code - which does 4K at
a time.

The fix is to ask for the maxium the driver can handle.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/mpage.c

@@ -290,7 +290,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 alloc_new:
 	if (bio == NULL) {
 		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-					nr_pages, GFP_KERNEL);
+			  	min_t(int, nr_pages, bio_get_nr_vecs(bdev)),
+				GFP_KERNEL);
 		if (bio == NULL)
 			goto confused;
 	}