[PATCH] direct-io: size the BIOs more accurately

We're being lazy when calculating the size of the needed BIO, allocating
two extra pages to cope with funny alignments.

Change that to be exact, thus allocating smaller BIOs someties.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/direct-io.c

@@ -954,8 +954,12 @@ direct_io_worker(int rw, struct kiocb *iocb, struct inode *inode,
 	dio->waiter = NULL;
 
 	dio->pages_in_io = 0;
-	for (seg = 0; seg < nr_segs; seg++) 
-		dio->pages_in_io += (iov[seg].iov_len >> blkbits) + 2; 
+	for (seg = 0; seg < nr_segs; seg++) {
+		user_addr = (unsigned long)iov[seg].iov_base;
+		dio->pages_in_io +=
+			((user_addr+iov[seg].iov_len +PAGE_SIZE-1)/PAGE_SIZE
+				- user_addr/PAGE_SIZE);
+	}
 
 	for (seg = 0; seg < nr_segs; seg++) {
 		user_addr = (unsigned long)iov[seg].iov_base;