xfs: avoid cil push lock if possible

Because now it hurts when the CIL fills up.

  - 37.20% __xfs_trans_commit
      - 35.84% xfs_log_commit_cil
         - 19.34% _raw_spin_lock
            - do_raw_spin_lock
                 19.01% __pv_queued_spin_lock_slowpath
         - 4.20% xfs_log_ticket_ungrant
              0.90% xfs_log_space_wake

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
index 8bb251d..78f8537 100644 (file)
--- a/fs/xfs/xfs_log_cil.c
+++ b/fs/xfs/xfs_log_cil.c
@@ -1422,10 +1422,18 @@ xlog_cil_push_background(
        ASSERT(!test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
 
        /*
-        * Don't do a background push if we haven't used up all the
-        * space available yet.
+        * We are done if:
+        * - we haven't used up all the space available yet; or
+        * - we've already queued up a push; and
+        * - we're not over the hard limit; and
+        * - nothing has been over the hard limit.
+        *
+        * If so, we don't need to take the push lock as there's nothing to do.
         */
-       if (space_used < XLOG_CIL_SPACE_LIMIT(log)) {
+       if (space_used < XLOG_CIL_SPACE_LIMIT(log) ||
+           (cil->xc_push_seq == cil->xc_current_sequence &&
+            space_used < XLOG_CIL_BLOCKING_SPACE_LIMIT(log) &&
+            !waitqueue_active(&cil->xc_push_wait))) {
                up_read(&cil->xc_ctx_lock);
                return;
        }