xfs: revert to using a kthread for AIL pushing

Currently we have a few issues with the way the workqueue code is used to
implement AIL pushing:

 - it accidentally uses the same workqueue as the syncer action, and thus
   can be prevented from running if there are enough sync actions active
   in the system.
 - it doesn't use the HIGHPRI flag to queue at the head of the queue of
   work items

At this point I'm not confident enough in getting all the workqueue flags and
tweaks right to provide a perfectly reliable execution context for AIL
pushing, which is the most important piece in XFS to make forward progress
when the log fills.

Revert back to use a kthread per filesystem which fixes all the above issues
at the cost of having a task struct and stack around for each mounted
filesystem.  In addition this also gives us much better ways to diagnose
any issues involving hung AIL pushing and removes a small amount of code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Stefan Priebe <s.priebe@profihost.ag>
Tested-by: Stefan Priebe <s.priebe@profihost.ag>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 1 insertions, 7 deletions

diff --git a/fs/xfs/xfs_trans_priv.h b/fs/xfs/xfs_trans_priv.h
index 212946b97239..22750b5e4a8f 100644
--- a/fs/xfs/xfs_trans_priv.h
+++ b/fs/xfs/xfs_trans_priv.h
@@ -64,23 +64,17 @@ struct xfs_ail_cursor {
  */
 struct xfs_ail {
         struct xfs_mount        *xa_mount;
+        struct task_struct      *xa_task;
         struct list_head        xa_ail;
         xfs_lsn_t               xa_target;
         struct list_head        xa_cursors;
         spinlock_t              xa_lock;
-        struct delayed_work     xa_work;
         xfs_lsn_t               xa_last_pushed_lsn;
-        unsigned long           xa_flags;
 };
 
-#define XFS_AIL_PUSHING_BIT     0
-
 /*
  * From xfs_trans_ail.c
  */
-
-extern struct workqueue_struct  *xfs_ail_wq;    /* AIL workqueue */
-
 void    xfs_trans_ail_update_bulk(struct xfs_ail *ailp,
                                 struct xfs_ail_cursor *cur,
                                 struct xfs_log_item **log_items, int nr_items,