On Wed 24-05-17 11:41:45, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> Find out if the write will trigger a wait due to writeback. If yes,
> return -EAGAIN.
>
> Return -EINVAL for buffered AIO: there are multiple causes of
> delay such as page locks, dirty throttling logic, page loading
> from disk etc. which cannot be taken care of.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/filemap.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 097213275461..bc146efa6815 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2675,6 +2675,9 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
>
> pos = iocb->ki_pos;
>
> + if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
> + return -EINVAL;
> +
> if (limit != RLIM_INFINITY) {
> if (iocb->ki_pos >= limit) {
> send_sig(SIGXFSZ, current, 0);
> @@ -2743,9 +2746,17 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from)
> write_len = iov_iter_count(from);
> end = (pos + write_len - 1) >> PAGE_SHIFT;
>
> - written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
> - if (written)
> - goto out;
> + if (iocb->ki_flags & IOCB_NOWAIT) {
> + /* If there are pages to writeback, return */
> + if (filemap_range_has_page(inode->i_mapping, pos,
> + pos + iov_iter_count(from)))
> + return -EAGAIN;
> + } else {
> + written = filemap_write_and_wait_range(mapping, pos,
> + pos + write_len - 1);
> + if (written)
> + goto out;
> + }
>
> /*
> * After a write we want buffered reads to be sure to go to disk to get
> --
> 2.12.0
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
