On Thu, Jun 17, 2021 at 06:35:49PM +0800, Ming Lei wrote:
> + /*
> + * Only support bio polling for normal IO, and the target io is
> + * exactly inside the dm io instance
> + */
> + ci->io->submit_as_polled = !!(ci->bio->bi_opf & REQ_POLLED);
Nit: the !! is not needed.
> @@ -1608,6 +1625,22 @@ static void init_clone_info(struct clone_info *ci,
> struct mapped_device *md,
> ci->map = map;
> ci->io = alloc_io(md, bio);
> ci->sector = bio->bi_iter.bi_sector;
> +
> + if (bio->bi_opf & REQ_POLLED) {
> + INIT_HLIST_NODE(&ci->io->node);
> +
> + /*
> + * Save .bi_end_io into dm_io, so that we can reuse .bi_end_io
> + * for storing dm_io list
> + */
> + if (bio->bi_opf & REQ_SAVED_END_IO) {
> + ci->io->saved_bio_end_io = NULL;
So if it already was saved the list gets cleared here? Can you explain
this logic a little more?
> + } else {
> + ci->io->saved_bio_end_io = bio->bi_end_io;
> + INIT_HLIST_HEAD((struct hlist_head *)&bio->bi_end_io);
I think you want to hide these casts in helpers that clearly document
why this is safe rather than sprinkling the casts all over the code.
I also wonder if there is any better way to structur this.
> +static int dm_poll_bio(struct bio *bio, unsigned int flags)
> +{
> + struct dm_io *io;
> + void *saved_bi_end_io = NULL;
> + struct hlist_head tmp = HLIST_HEAD_INIT;
> + struct hlist_head *head = (struct hlist_head *)&bio->bi_end_io;
> + struct hlist_node *next;
> +
> + /*
> + * This bio can be submitted from FS as POLLED so that FS may keep
> + * polling even though the flag is cleared by bio splitting or
> + * requeue, so return immediately.
> + */
> + if (!(bio->bi_opf & REQ_POLLED))
> + return 0;
I can't really parse the comment, can you explain this a little more?
But if we need this check, shouldn't it move to bio_poll()?
> + hlist_for_each_entry(io, &tmp, node) {
> + if (io->saved_bio_end_io && !saved_bi_end_io) {
> + saved_bi_end_io = io->saved_bio_end_io;
> + break;
> + }
> + }
So it seems like you don't use bi_cookie at all. Why not turn
bi_cookie into a union to stash the hlist_head and use that?
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