From: "Darrick J. Wong" <djwong@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
Jeffle Xu <jefflexu@linux.alibaba.com>,
Ming Lei <ming.lei@redhat.com>,
Damien Le Moal <Damien.LeMoal@wdc.com>,
Keith Busch <kbusch@kernel.org>, Sagi Grimberg <sagi@grimberg.me>,
"Wunderlich, Mark" <mark.wunderlich@intel.com>,
"Vasudevan, Anil" <anil.vasudevan@intel.com>,
linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-nvme@lists.infradead.org
Subject: Re: [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw
Date: Wed, 12 May 2021 14:32:30 -0700 [thread overview]
Message-ID: <20210512213230.GB8543@magnolia> (raw)
In-Reply-To: <20210512131545.495160-4-hch@lst.de>
On Wed, May 12, 2021 at 03:15:33PM +0200, Christoph Hellwig wrote:
> If an iocb is split into multiple bios we can't poll for both. So don't
> bother to even try to poll in that case.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
Ahh the fun of reviewing things like iopoll that I'm not all /that/
familiar with...
> ---
> fs/iomap/direct-io.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 9398b8c31323..d5637f467109 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -282,6 +282,13 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> if (!iov_iter_count(dio->submit.iter))
> goto out;
>
> + /*
> + * We can only poll for single bio I/Os.
> + */
> + if (need_zeroout ||
> + ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
Hm, is this logic here to catch the second iomap_dio_zero below the
zero_tail: label? What happens if we have an unaligned direct write
that starts below EOF but (for whatever reason) ends the loop with pos
now above EOF but not on a block boundary?
> + dio->iocb->ki_flags &= ~IOCB_HIPRI;
> +
> if (need_zeroout) {
> /* zero out from the start of the block to the write offset */
> pad = pos & (fs_block_size - 1);
> @@ -339,6 +346,11 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>
> nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
> BIO_MAX_VECS);
> + /*
> + * We can only poll for single bio I/Os.
> + */
> + if (nr_pages)
> + dio->iocb->ki_flags &= ~IOCB_HIPRI;
> iomap_dio_submit_bio(dio, iomap, bio, pos);
> pos += n;
> } while (nr_pages);
> @@ -579,6 +591,11 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> iov_iter_revert(iter, pos - dio->i_size);
> break;
> }
> +
> + /*
> + * We can only poll for single bio I/Os.
> + */
> + iocb->ki_flags &= ~IOCB_HIPRI;
Hmm, why is this here? Won't this clear IOCB_HIPRI even if the first
iomap_apply call successfully creates a polled bio for the entire iovec
such that we exit the loop one line later because count becomes zero?
How does the upper layer (io_uring, I surmise?) know that there's
a bio that it should poll for?
<shrug> Unless the only effect that this has is making it so that the
subsequent calls to iomap_apply don't have the polling mode set? I see
enough places in io_uring.c that check (iocb->ki_flags & IOCB_HIPRI) to
make me wonder if the lifetime of that flag ends as soon as we get to
->{read,write}_iter?
--D
> } while ((count = iov_iter_count(iter)) > 0);
> blk_finish_plug(&plug);
>
> --
> 2.30.2
>
next prev parent reply other threads:[~2021-05-12 21:41 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
2021-05-12 13:15 ` [PATCH 01/15] direct-io: remove blk_poll support Christoph Hellwig
2021-05-12 13:15 ` [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO Christoph Hellwig
2021-05-12 20:54 ` Sagi Grimberg
2021-05-16 18:01 ` Kanchan Joshi
2021-05-12 13:15 ` [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw Christoph Hellwig
2021-05-12 21:32 ` Darrick J. Wong [this message]
2021-05-12 13:15 ` [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper Christoph Hellwig
2021-05-12 20:58 ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 05/15] blk-mq: factor out a "classic" poll helper Christoph Hellwig
2021-05-12 20:59 ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal Christoph Hellwig
2021-05-12 21:42 ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 07/15] blk-mq: remove blk_qc_t_valid Christoph Hellwig
2021-05-12 21:43 ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 08/15] io_uring: don't sleep when polling for I/O Christoph Hellwig
2021-05-12 21:55 ` Sagi Grimberg
2021-05-19 13:02 ` Christoph Hellwig
2021-05-12 13:15 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig
2021-05-12 21:56 ` Sagi Grimberg
2021-05-12 22:43 ` Chaitanya Kulkarni
2021-05-12 13:15 ` [PATCH 10/15] block: use SLAB_TYPESAFE_BY_RCU for the bio slab Christoph Hellwig
2021-05-12 13:15 ` [PATCH 11/15] block: define 'struct bvec_iter' as packed Christoph Hellwig
2021-05-12 21:58 ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 12/15] block: switch polling to be bio based Christoph Hellwig
2021-05-12 22:03 ` Sagi Grimberg
2021-05-12 22:12 ` Keith Busch
2021-05-14 2:50 ` Keith Busch
2021-05-14 16:26 ` Keith Busch
2021-05-14 16:28 ` Christoph Hellwig
2021-05-13 1:26 ` Ming Lei
2021-05-13 1:23 ` Ming Lei
2021-05-12 13:15 ` [PATCH 13/15] block: don't allow writing to the poll queue attribute Christoph Hellwig
2021-05-12 22:04 ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 14/15] nvme-multipath: set QUEUE_FLAG_NOWAIT Christoph Hellwig
2021-05-12 13:15 ` [PATCH 15/15] nvme-multipath: enable polled I/O Christoph Hellwig
2021-05-12 22:10 ` Sagi Grimberg
2021-05-12 22:16 ` Keith Busch
2021-05-13 23:33 ` switch block layer polling to a bio based model v3 Wunderlich, Mark
-- strict thread matches above, loose matches on Subject: below --
2021-04-27 16:16 switch block layer polling to a bio based model v2 Christoph Hellwig
2021-04-27 16:16 ` [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw Christoph Hellwig
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