xfs: move inode flush to the sync workqueue

Move the inode dirty data flushing to a workqueue so that multiple
threads can take advantage of a single thread's flushing work.  The
ratelimiting technique used in bdd4ee4 was not successful, because
threads that skipped the inode flush scan due to ratelimiting would
ENOSPC early, which caused occasional (but noticeable) changes in
behavior and sporadic fstest regressions.

Therefore, make all the writer threads wait on a single inode flush,
which eliminates both the stampeding hordes of flushers and the small
window in which a write could fail with ENOSPC because it lost the
ratelimit race after even another thread freed space.

Fixes: c6425702f21e ("xfs: ratelimit inode flush on buffered write ENOSPC")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 50c43422fa17..b2e4598fdf7d 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -167,8 +167,12 @@ typedef struct xfs_mount {
 	struct xfs_kobj		m_error_meta_kobj;
 	struct xfs_error_cfg	m_error_cfg[XFS_ERR_CLASS_MAX][XFS_ERR_ERRNO_MAX];
 	struct xstats		m_stats;	/* per-fs stats */
-	struct ratelimit_state	m_flush_inodes_ratelimit;
 
+	/*
+	 * Workqueue item so that we can coalesce multiple inode flush attempts
+	 * into a single flush.
+	 */
+	struct work_struct	m_flush_inodes_work;
 	struct workqueue_struct *m_buf_workqueue;
 	struct workqueue_struct	*m_unwritten_workqueue;
 	struct workqueue_struct	*m_cil_workqueue;