xfs: split metadata and log buffer completion to separate workqueues

XFS traditionally sends all buffer I/O completion work to a single
workqueue. This includes metadata buffer completion and log buffer
completion. The log buffer completion requires a high priority queue to
prevent stalls due to log forces getting stuck behind other queued work.

Rather than continue to prioritize all buffer I/O completion due to the
needs of log completion, split log buffer completion off to
m_log_workqueue and move the high priority flag from m_buf_workqueue to
m_log_workqueue.

Add a b_ioend_wq wq pointer to xfs_buf to allow completion workqueue
customization on a per-buffer basis. Initialize b_ioend_wq to
m_buf_workqueue by default in the generic buffer I/O submission path.
Finally, override the default wq with the high priority m_log_workqueue
in the log buffer I/O submission path.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

4 files changed, 18 insertions, 7 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index d083889535a2..945bea924e48 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1041,7 +1041,7 @@ xfs_buf_ioend_work(
         struct work_struct      *work)
 {
         struct xfs_buf          *bp =
-                container_of(work, xfs_buf_t, b_iodone_work);
+                container_of(work, xfs_buf_t, b_ioend_work);
 
         xfs_buf_ioend(bp);
 }
@@ -1050,8 +1050,8 @@ void
 xfs_buf_ioend_async(
         struct xfs_buf  *bp)
 {
-        INIT_WORK(&bp->b_iodone_work, xfs_buf_ioend_work);
-        queue_work(bp->b_target->bt_mount->m_buf_workqueue, &bp->b_iodone_work);
+        INIT_WORK(&bp->b_ioend_work, xfs_buf_ioend_work);
+        queue_work(bp->b_ioend_wq, &bp->b_ioend_work);
 }
 
 void
@@ -1220,6 +1220,13 @@ _xfs_buf_ioapply(
          */
         bp->b_error = 0;
 
+        /*
+         * Initialize the I/O completion workqueue if we haven't yet or the
+         * submitter has not opted to specify a custom one.
+         */
+        if (!bp->b_ioend_wq)
+                bp->b_ioend_wq = bp->b_target->bt_mount->m_buf_workqueue;
+
         if (bp->b_flags & XBF_WRITE) {
                 if (bp->b_flags & XBF_SYNCIO)
                         rw = WRITE_SYNC;
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 82002c00af90..75ff5d5a7d2e 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -164,7 +164,8 @@ typedef struct xfs_buf {
         struct xfs_perag        *b_pag;         /* contains rbtree root */
         xfs_buftarg_t           *b_target;      /* buffer target (device) */
         void                    *b_addr;        /* virtual address of buffer */
-        struct work_struct      b_iodone_work;
+        struct work_struct      b_ioend_work;
+        struct workqueue_struct *b_ioend_wq;    /* I/O completion wq */
         xfs_buf_iodone_t        b_iodone;       /* I/O completion function */
         struct completion       b_iowait;       /* queue for I/O waiters */
         void                    *b_fspriv;
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index e810e9df91b7..d508a654e198 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -1808,6 +1808,8 @@ xlog_sync(
         XFS_BUF_ZEROFLAGS(bp);
         XFS_BUF_ASYNC(bp);
         bp->b_flags |= XBF_SYNCIO;
+        /* use high priority completion wq */
+        bp->b_ioend_wq = log->l_mp->m_log_workqueue;
 
         if (log->l_mp->m_flags & XFS_MOUNT_BARRIER) {
                 bp->b_flags |= XBF_FUA;
@@ -1856,6 +1858,8 @@ xlog_sync(
                 bp->b_flags |= XBF_SYNCIO;
                 if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)
                         bp->b_flags |= XBF_FUA;
+                /* use high priority completion wq */
+                bp->b_ioend_wq = log->l_mp->m_log_workqueue;
 
                 ASSERT(XFS_BUF_ADDR(bp) <= log->l_logBBsize-1);
                 ASSERT(XFS_BUF_ADDR(bp) + BTOBB(count) <= log->l_logBBsize);
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 45fa5b570eb5..b5aacfc462af 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -842,8 +842,7 @@ xfs_init_mount_workqueues(
         struct xfs_mount        *mp)
 {
         mp->m_buf_workqueue = alloc_workqueue("xfs-buf/%s",
-                        WQ_MEM_RECLAIM|WQ_HIGHPRI|WQ_FREEZABLE, 1,
-                        mp->m_fsname);
+                        WQ_MEM_RECLAIM|WQ_FREEZABLE, 1, mp->m_fsname);
         if (!mp->m_buf_workqueue)
                 goto out;
 
@@ -868,7 +867,7 @@ xfs_init_mount_workqueues(
                 goto out_destroy_cil;
 
         mp->m_log_workqueue = alloc_workqueue("xfs-log/%s",
-                        WQ_FREEZABLE, 0, mp->m_fsname);
+                        WQ_FREEZABLE|WQ_HIGHPRI, 0, mp->m_fsname);
         if (!mp->m_log_workqueue)
                 goto out_destroy_reclaim;