On Mon, Feb 17, 2025 at 10:31:26AM +0100, Christoph Hellwig wrote:
> Currently all metadata I/O completions happen in the m_buf_workqueue
> workqueue. But for synchronous I/O (i.e. all buffer reads) there is no
> need for that, as there always is a called in process context that is
> waiting for the I/O. Factor out the guts of xfs_buf_ioend into a
> separate helper and call it from xfs_buf_iowait to avoid a double
> an extra context switch to the workqueue.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/xfs/xfs_buf.c | 42 ++++++++++++++++++++++++++----------------
> 1 file changed, 26 insertions(+), 16 deletions(-)
>
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 15bb790359f8..050f2c2f6a40 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1345,6 +1345,7 @@ xfs_buf_ioend_handle_error(
> resubmit:
> xfs_buf_ioerror(bp, 0);
> bp->b_flags |= (XBF_DONE | XBF_WRITE_FAIL);
> + reinit_completion(&bp->b_iowait);
> xfs_buf_submit(bp);
> return true;
> out_stale:
> @@ -1355,8 +1356,8 @@ xfs_buf_ioend_handle_error(
> return false;
> }
>
> -static void
> -xfs_buf_ioend(
> +static bool
> +__xfs_buf_ioend(
What does the return value here indicate? I /think/ it's true if the IO
is really complete, or false if we're going to retry? But maybe it
actually means true if the bp reference is still live? A comment would
be really helpful here.
--D
> struct xfs_buf *bp)
> {
> trace_xfs_buf_iodone(bp, _RET_IP_);
> @@ -1376,7 +1377,7 @@ xfs_buf_ioend(
> }
>
> if (unlikely(bp->b_error) && xfs_buf_ioend_handle_error(bp))
> - return;
> + return false;
>
> /* clear the retry state */
> bp->b_last_error = 0;
> @@ -1397,7 +1398,15 @@ xfs_buf_ioend(
>
> bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD |
> _XBF_LOGRECOVERY);
> + return true;
> +}
>
> +static void
> +xfs_buf_ioend(
> + struct xfs_buf *bp)
> +{
> + if (!__xfs_buf_ioend(bp))
> + return;
> if (bp->b_flags & XBF_ASYNC)
> xfs_buf_relse(bp);
> else
> @@ -1411,15 +1420,8 @@ xfs_buf_ioend_work(
> struct xfs_buf *bp =
> container_of(work, struct xfs_buf, b_ioend_work);
>
> - xfs_buf_ioend(bp);
> -}
> -
> -static void
> -xfs_buf_ioend_async(
> - struct xfs_buf *bp)
> -{
> - INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
> - queue_work(bp->b_mount->m_buf_workqueue, &bp->b_ioend_work);
> + if (__xfs_buf_ioend(bp))
> + xfs_buf_relse(bp);
> }
>
> void
> @@ -1491,7 +1493,13 @@ xfs_buf_bio_end_io(
> XFS_TEST_ERROR(false, bp->b_mount, XFS_ERRTAG_BUF_IOERROR))
> xfs_buf_ioerror(bp, -EIO);
>
> - xfs_buf_ioend_async(bp);
> + if (bp->b_flags & XBF_ASYNC) {
> + INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
> + queue_work(bp->b_mount->m_buf_workqueue, &bp->b_ioend_work);
> + } else {
> + complete(&bp->b_iowait);
> + }
> +
> bio_put(bio);
> }
>
> @@ -1568,9 +1576,11 @@ xfs_buf_iowait(
> {
> ASSERT(!(bp->b_flags & XBF_ASYNC));
>
> - trace_xfs_buf_iowait(bp, _RET_IP_);
> - wait_for_completion(&bp->b_iowait);
> - trace_xfs_buf_iowait_done(bp, _RET_IP_);
> + do {
> + trace_xfs_buf_iowait(bp, _RET_IP_);
> + wait_for_completion(&bp->b_iowait);
> + trace_xfs_buf_iowait_done(bp, _RET_IP_);
> + } while (!__xfs_buf_ioend(bp));
>
> return bp->b_error;
> }
> --
> 2.45.2
>
>
