[PATCH] DAX: use proper length when the range is not aligned to PAGE_SIZE

[Liu Bo <bo.li.liu@oracle.com>]

Currently if we write to [2k, 6k] where pos is 2k and end is 6k,
get_block() will be called twice, but we can save one get_block
by sending two blocks together to get_block.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
---
 fs/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index 53eb6a0..8d4bd5f 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -172,7 +172,7 @@ static ssize_t dax_io(struct inode *inode, struct iov_iter *iter,
 			long size;
 
 			if (pos == bh_max) {
-				bh->b_size = PAGE_ALIGN(end - pos);
+				bh->b_size = PAGE_ALIGN(end - (pos - first));
 				bh->b_state = 0;
 				rc = get_block(inode, block, bh, rw == WRITE);
 				if (rc)
-- 
2.5.5