On Tue, Mar 04, 2025 at 12:18:07PM +0000, Pavel Begunkov wrote:
> ((dio->flags & IOMAP_DIO_NEED_SYNC) && !use_fua) ||
> - ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
> + ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode))) {
> dio->flags &= ~IOMAP_DIO_CALLER_COMP;
>
> + if (!is_sync_kiocb(dio->iocb) &&
> + (dio->iocb->ki_flags & IOCB_NOWAIT))
> + return -EAGAIN;
Black magic without comments explaining it.
> + if (!is_sync_kiocb(dio->iocb) && (dio->iocb->ki_flags & IOCB_NOWAIT)) {
> + /*
> + * This is nonblocking IO, and we might need to allocate
> + * multiple bios. In this case, as we cannot guarantee that
> + * one of the sub bios will not fail getting issued FOR NOWAIT
> + * and as error results are coalesced across all of them, ask
> + * for a retry of this from blocking context.
> + */
> + if (bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS + 1) >
> + BIO_MAX_VECS)
This is not very accurate in times of multi-page bvecs and large order
folios all over.
I think you really need to byte the bullet and support for early returns
from the non-blocking bio submission path.
