xfs: allow assigning the tail lsn with the AIL lock held

Provide a variant of xlog_assign_tail_lsn that has the AIL lock already
held.  By doing so we do an additional atomic_read + atomic_set under
the lock, which comes down to two instructions.

Switch xfs_trans_ail_update_bulk and xfs_trans_ail_delete_bulk to the
new version to reduce the number of lock roundtrips, and prepare for
a new addition that would require a third lock roundtrip in
xfs_trans_ail_delete_bulk.  This addition is also the reason for
slightly rearranging the conditionals and relying on xfs_log_space_wake
for checking that the filesystem has been shut down internally.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 15 insertions, 7 deletions

diff --git a/fs/xfs/xfs_trans_ail.c b/fs/xfs/xfs_trans_ail.c
index 1dead07f092c..77acc53f2f31 100644
--- a/fs/xfs/xfs_trans_ail.c
+++ b/fs/xfs/xfs_trans_ail.c
@@ -79,7 +79,7 @@ xfs_ail_check(
  * Return a pointer to the first item in the AIL.  If the AIL is empty, then
  * return NULL.
  */
-static xfs_log_item_t *
+xfs_log_item_t *
 xfs_ail_min(
         struct xfs_ail  *ailp)
 {
@@ -667,11 +667,15 @@ xfs_trans_ail_update_bulk(
 
         if (!list_empty(&tmp))
                 xfs_ail_splice(ailp, cur, &tmp, lsn);
-        spin_unlock(&ailp->xa_lock);
 
-        if (mlip_changed && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
-                xlog_assign_tail_lsn(ailp->xa_mount);
+        if (mlip_changed) {
+                if (!XFS_FORCED_SHUTDOWN(ailp->xa_mount))
+                        xlog_assign_tail_lsn_locked(ailp->xa_mount);
+                spin_unlock(&ailp->xa_lock);
+
                 xfs_log_space_wake(ailp->xa_mount);
+        } else {
+                spin_unlock(&ailp->xa_lock);
         }
 }
 
@@ -729,11 +733,15 @@ xfs_trans_ail_delete_bulk(
                 if (mlip == lip)
                         mlip_changed = 1;
         }
-        spin_unlock(&ailp->xa_lock);
 
-        if (mlip_changed && !XFS_FORCED_SHUTDOWN(ailp->xa_mount)) {
-                xlog_assign_tail_lsn(ailp->xa_mount);
+        if (mlip_changed) {
+                if (!XFS_FORCED_SHUTDOWN(ailp->xa_mount))
+                        xlog_assign_tail_lsn_locked(ailp->xa_mount);
+                spin_unlock(&ailp->xa_lock);
+
                 xfs_log_space_wake(ailp->xa_mount);
+        } else {
+                spin_unlock(&ailp->xa_lock);
         }
 }