Re: [PATCH 17/28] xfs: synchronous AIL pushing

Brian Foster
2019-11-05T17:05:14Z

On Fri, Nov 01, 2019 at 10:46:07AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Provide an interface to push the AIL to a target LSN and wait for
> the tail of the log to move past that LSN. This is used to wait for
> all items older than a specific LSN to either be cleaned (written
> back) or relogged to a higher LSN in the AIL. The primary use for
> this is to allow IO free inode reclaim throttling.
>
> Factor the common AIL deletion code that does all the wakeups into a
> helper so we only have one copy of this somewhat tricky code to
> interface with all the wakeups necessary when the LSN of the log
> tail changes.
>

The above paragraph doesn't seem applicable to this patch. With that
fixed:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> xfs_ail_push_sync() is temporary infrastructure to facilitate
> non-blocking, IO-less inode reclaim throttling that allows further
> structural changes to be made. Once those structural changes are
> made, the need for this function goes away and it is removed. In
> essence, it is only provided to ensure git bisects don't break while
> the changes to the reclaim algorithms are in progress.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_trans_ail.c | 32 ++++++++++++++++++++++++++++++++
> fs/xfs/xfs_trans_priv.h | 2 ++
> 2 files changed, 34 insertions(+)
>
> diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
> index 685a21cd24c0..3e1d0e1439e2 100644
> --- a/fs/xfs/xfs_trans_ail.c
> +++ b/fs/xfs/xfs_trans_ail.c
> @@ -662,6 +662,36 @@ xfs_ail_push_all(
> xfs_ail_push(ailp, threshold_lsn);
> }
>
> +/*
> + * Push the AIL to a specific lsn and wait for it to complete.
> + */
> +void
> +xfs_ail_push_sync(
> + struct xfs_ail *ailp,
> + xfs_lsn_t threshold_lsn)
> +{
> + struct xfs_log_item *lip;
> + DEFINE_WAIT(wait);
> +
> + spin_lock(&ailp->ail_lock);
> + while ((lip = xfs_ail_min(ailp)) != NULL) {
> + prepare_to_wait(&ailp->ail_push, &wait, TASK_UNINTERRUPTIBLE);
> + if (XFS_FORCED_SHUTDOWN(ailp->ail_mount) ||
> + XFS_LSN_CMP(threshold_lsn, lip->li_lsn) < 0)
> + break;
> + if (XFS_LSN_CMP(threshold_lsn, ailp->ail_target) > 0)
> + ailp->ail_target = threshold_lsn;
> + wake_up_process(ailp->ail_task);
> + spin_unlock(&ailp->ail_lock);
> + schedule();
> + spin_lock(&ailp->ail_lock);
> + }
> + spin_unlock(&ailp->ail_lock);
> +
> + finish_wait(&ailp->ail_push, &wait);
> +}
> +
> +
> /*
> * Push out all items in the AIL immediately and wait until the AIL is empty.
> */
> @@ -702,6 +732,7 @@ xfs_ail_update_finish(
> if (!XFS_FORCED_SHUTDOWN(mp))
> xlog_assign_tail_lsn_locked(mp);
>
> + wake_up_all(&ailp->ail_push);
> if (list_empty(&ailp->ail_head))
> wake_up_all(&ailp->ail_empty);
> spin_unlock(&ailp->ail_lock);
> @@ -858,6 +889,7 @@ xfs_trans_ail_init(
> spin_lock_init(&ailp->ail_lock);
> INIT_LIST_HEAD(&ailp->ail_buf_list);
> init_waitqueue_head(&ailp->ail_empty);
> + init_waitqueue_head(&ailp->ail_push);
>
> ailp->ail_task = kthread_run(xfsaild, ailp, "xfsaild/%s",
> ailp->ail_mount->m_fsname);
> diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
> index 35655eac01a6..1b6f4bbd47c0 100644
> --- a/fs/xfs/xfs_trans_priv.h
> +++ b/fs/xfs/xfs_trans_priv.h
> @@ -61,6 +61,7 @@ struct xfs_ail {
> int ail_log_flush;
> struct list_head ail_buf_list;
> wait_queue_head_t ail_empty;
> + wait_queue_head_t ail_push;
> };
>
> /*
> @@ -113,6 +114,7 @@ xfs_trans_ail_remove(
> }
>
> void xfs_ail_push(struct xfs_ail *, xfs_lsn_t);
> +void xfs_ail_push_sync(struct xfs_ail *, xfs_lsn_t);
> void xfs_ail_push_all(struct xfs_ail *);
> void xfs_ail_push_all_sync(struct xfs_ail *);
> struct xfs_log_item *xfs_ail_min(struct xfs_ail *ailp);
> --
> 2.24.0.rc0
>