zvol_remove_minors do parallel zvol_free

On some kernel version, blk_cleanup_queue and put_disk will wait for more then
10ms. So a pool with a lot of zvols will easily wait for more then 1 min if we
do zvol_free sequentially.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Requires-spl: refs/pull/588/head

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 8bc0a608ced5605e8d3d6df799126f67521a15e2..61d0538a34a4a090b9ba514f13bd4851d97ba0bc 100644 (file)
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -1036,7 +1036,7 @@ zvol_open(struct block_device *bdev, fmode_t flag)
 
        /*
         * Obtain a copy of private_data under the lock to make sure
-        * that either the result of zvol_freeg() setting
+        * that either the result of zvol_free() setting
         * bdev->bd_disk->private_data to NULL is observed, or zvol_free()
         * is not called on this zv because of the positive zv_open_count.
         */
@@ -1316,12 +1316,13 @@ out_kmem:
 }
 
 /*
- * Cleanup then free a zvol_state_t which was created by zvol_alloc().
+ * Used for taskq, if used out side zvol_state_lock, you need to clear
+ * zv_disk->private_data inside lock first.
  */
 static void
-zvol_free(zvol_state_t *zv)
+zvol_free_impl(void *arg)
 {
-       ASSERT(MUTEX_HELD(&zvol_state_lock));
+       zvol_state_t *zv = arg;
        ASSERT(zv->zv_open_count == 0);
 
        zfs_rlock_destroy(&zv->zv_range_lock);
@@ -1336,6 +1337,16 @@ zvol_free(zvol_state_t *zv)
        kmem_free(zv, sizeof (zvol_state_t));
 }
 
+/*
+ * Cleanup then free a zvol_state_t which was created by zvol_alloc().
+ */
+static void
+zvol_free(zvol_state_t *zv)
+{
+       ASSERT(MUTEX_HELD(&zvol_state_lock));
+       zvol_free_impl(zv);
+}
+
 /*
  * Create a block device minor node and setup the linkage between it
  * and the specified volume.  Once this function returns the block
@@ -1691,6 +1702,7 @@ zvol_remove_minors_impl(const char *name)
 {
        zvol_state_t *zv, *zv_next;
        int namelen = ((name) ? strlen(name) : 0);
+       taskqid_t t, tid = TASKQID_INVALID;
 
        if (zvol_inhibit_dev)
                return;
@@ -1710,11 +1722,22 @@ zvol_remove_minors_impl(const char *name)
                                continue;
 
                        zvol_remove(zv);
-                       zvol_free(zv);
+
+                       /* clear this so zvol_open won't open it */
+                       zv->zv_disk->private_data = NULL;
+
+                       /* try parallel zv_free, if failed do it in place */
+                       t = taskq_dispatch(system_taskq, zvol_free_impl, zv,
+                           TQ_SLEEP);
+                       if (t == TASKQID_INVALID)
+                               zvol_free(zv);
+                       else
+                               tid = t;
                }
        }
-
        mutex_exit(&zvol_state_lock);
+       if (tid != TASKQID_INVALID)
+               taskq_wait_outstanding(system_taskq, tid);
 }
 
 /* Remove minor for this specific snapshot only */