4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>

*** 1786,1812 ****
          }
          mutex_exit(&dn->dn_mtx);
  }
  
  /*
!  * Call when we think we're going to write/free space in open context.
!  * Be conservative (ie. OK to write less than this or free more than
!  * this, but don't write more or free less).
   */
  void
  dnode_willuse_space(dnode_t *dn, int64_t space, dmu_tx_t *tx)
  {
          objset_t *os = dn->dn_objset;
          dsl_dataset_t *ds = os->os_dsl_dataset;
  
!         if (space > 0)
!                 space = spa_get_asize(os->os_spa, space);
  
!         if (ds)
!                 dsl_dir_willuse_space(ds->ds_dir, space, tx);
! 
!         dmu_tx_willuse_space(tx, space);
  }
  
  /*
   * Scans a block at the indicated "level" looking for a hole or data,
   * depending on 'flags'.
--- 1786,1811 ----
          }
          mutex_exit(&dn->dn_mtx);
  }
  
  /*
!  * Call when we think we're going to write/free space in open context to track
!  * the amount of memory in use by the currently open txg.
   */
  void
  dnode_willuse_space(dnode_t *dn, int64_t space, dmu_tx_t *tx)
  {
          objset_t *os = dn->dn_objset;
          dsl_dataset_t *ds = os->os_dsl_dataset;
+         int64_t aspace = spa_get_asize(os->os_spa, space);
  
!         if (ds != NULL) {
!                 dsl_dir_willuse_space(ds->ds_dir, aspace, tx);
!                 dsl_pool_dirty_space(dmu_tx_pool(tx), space, tx);
!         }
  
!         dmu_tx_willuse_space(tx, aspace);
  }
  
  /*
   * Scans a block at the indicated "level" looking for a hole or data,
   * depending on 'flags'.