On Sat, Oct 23, 2021 at 05:21:34PM +0100, Pavel Begunkov wrote:
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -352,11 +352,21 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
> bio->bi_end_io = blkdev_bio_end_io_async;
> bio->bi_ioprio = iocb->ki_ioprio;
>
> - ret = bio_iov_iter_get_pages(bio, iter);
> - if (unlikely(ret)) {
> - bio->bi_status = BLK_STS_IOERR;
> - bio_endio(bio);
> - return ret;
> + if (!iov_iter_is_bvec(iter)) {
> + ret = bio_iov_iter_get_pages(bio, iter);
> + if (unlikely(ret)) {
> + bio->bi_status = BLK_STS_IOERR;
> + bio_endio(bio);
> + return ret;
> + }
Nit: I generally find it much nicer to read if simple if statements
don't use pointless negations.
> + } else {
> + /*
> + * Users don't rely on the iterator being in any particular
> + * state for async I/O returning -EIOCBQUEUED, hence we can
> + * avoid expensive iov_iter_advance(). Bypass
> + * bio_iov_iter_get_pages() and set the bvec directly.
> + */
> + bio_iov_bvec_set(bio, iter);
So if this optimization is so useful, please also do it for
non-bvec iov_iters, which is what 99% of the applications actually
use.
