13389 After persistent L2ARC import, cache device has constant 8KB/sec load
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: Dan McDonald <danmcd@joyent.com>
Reviewed by: Toomas Soome <tsoome@me.com>

*** 8345,8354 ****
--- 8345,8355 ----
          uint64_t                write_asize, write_psize, write_lsize, headroom;
          boolean_t               full;
          l2arc_write_callback_t  *cb = NULL;
          zio_t                   *pio, *wzio;
          uint64_t                guid = spa_load_guid(spa);
+         l2arc_dev_hdr_phys_t    *l2dhdr = dev->l2ad_dev_hdr;
  
          ASSERT3P(dev->l2ad_vdev, !=, NULL);
  
          pio = NULL;
          write_lsize = write_asize = write_psize = 0;
*** 8563,8572 ****
--- 8564,8574 ----
  
                  /*
                   * Although we did not write any buffers l2ad_evict may
                   * have advanced.
                   */
+                 if (dev->l2ad_evict != l2dhdr->dh_evict)
                          l2arc_dev_hdr_update(dev);
  
                  return (0);
          }