On Tue, Dec 05, 2017 at 10:57:53AM -0500, Harish Kasiviswanathan wrote:
> The first write after file create fails to take the direct IO
> (Peer-to-Peer) path and falls back to slower software copy. The function
> get_more_block() sets 'create' to 0 after comparing 'unsigned long
> fs_startblk = 0' with 'long long (i_size_read(dio->inode) - 1) >>
> i_blkbits = 0xfffffffffffff'.
>
> Signed-off-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@xxxxxxx>
> ---
> fs/direct-io.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 3aafb33..588aa17 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -687,8 +687,8 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
> */
> create = dio->op == REQ_OP_WRITE;
> if (dio->flags & DIO_SKIP_HOLES) {
I think the major problem here is that the original code didn't consider
the i_size=0 case (my bad). Perhaps we can make sure i_size is greater
than 0 first? As what we want to avoid is "fill holes inside i_size",
and i_size == 0 means we're guaranteed not to allocate new blocks inside
i_size.
Thanks,
Eryu
> - if (fs_startblk <= ((i_size_read(dio->inode) - 1) >>
> - i_blkbits))
> + if ((loff_t)fs_startblk <=
> + ((i_size_read(dio->inode) - 1) >> i_blkbits))
> create = 0;
> }
>
> --
> 2.7.4
>
