NEX-19083 backport OS-7314 zil_commit should omit cache thrash
9962 zil_commit should omit cache thrash
Reviewed by: Matt Ahrens <matt@delphix.com>
Reviewed by: Brad Lewis <brad.lewis@delphix.com>
Reviewed by: Patrick Mooney <patrick.mooney@joyent.com>
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Approved by: Joshua M. Clulow <josh@sysmgr.org>

@@ -46,14 +46,15 @@
  *
  * After the lwb is "opened", it can transition into the "issued" state
  * via zil_lwb_write_issue(). Again, the zilog's "zl_issuer_lock" must
  * be held when making this transition.
  *
- * After the lwb's zio completes, and the vdev's are flushed, the lwb
- * will transition into the "done" state via zil_lwb_write_done(). When
- * transitioning from "issued" to "done", the zilog's "zl_lock" must be
- * held, *not* the "zl_issuer_lock".
+ * After the lwb's write zio completes, it transitions into the "write
+ * done" state via zil_lwb_write_done(); and then into the "flush done"
+ * state via zil_lwb_flush_vdevs_done(). When transitioning from
+ * "issued" to "write done", and then from "write done" to "flush done",
+ * the zilog's "zl_lock" must be held, *not* the "zl_issuer_lock".
  *
  * The zilog's "zl_issuer_lock" can become heavily contended in certain
  * workloads, so we specifically avoid acquiring that lock when
  * transitioning an lwb from "issued" to "done". This allows us to avoid
  * having to acquire the "zl_issuer_lock" for each lwb ZIO completion,

@@ -66,17 +67,18 @@
  *
  * Thus, if an lwb is in the "closed" or "opened" state, holding the
  * "zl_issuer_lock" will prevent a concurrent thread from transitioning
  * that lwb to the "issued" state. Likewise, if an lwb is already in the
  * "issued" state, holding the "zl_lock" will prevent a concurrent
- * thread from transitioning that lwb to the "done" state.
+ * thread from transitioning that lwb to the "write done" state.
  */
 typedef enum {
     LWB_STATE_CLOSED,
     LWB_STATE_OPENED,
     LWB_STATE_ISSUED,
-    LWB_STATE_DONE,
+    LWB_STATE_WRITE_DONE,
+    LWB_STATE_FLUSH_DONE,
     LWB_NUM_STATES
 } lwb_state_t;
 
 /*
  * Log write block (lwb)