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>

@@ -582,11 +582,10 @@
         return (myspace);
 }
 
 struct tempreserve {
         list_node_t tr_node;
-        dsl_pool_t *tr_dp;
         dsl_dir_t *tr_ds;
         uint64_t tr_size;
 };
 
 static int

@@ -733,29 +732,28 @@
                 struct tempreserve *tr;
 
                 tr = kmem_zalloc(sizeof (struct tempreserve), KM_SLEEP);
                 tr->tr_size = lsize;
                 list_insert_tail(tr_list, tr);
-
-                err = dsl_pool_tempreserve_space(dd->dd_pool, asize, tx);
         } else {
                 if (err == EAGAIN) {
+                        /*
+                         * If arc_memory_throttle() detected that pageout
+                         * is running and we are low on memory, we delay new
+                         * non-pageout transactions to give pageout an
+                         * advantage.
+                         *
+                         * It is unfortunate to be delaying while the caller's
+                         * locks are held.
+                         */
                         txg_delay(dd->dd_pool, tx->tx_txg,
                             MSEC2NSEC(10), MSEC2NSEC(10));
                         err = SET_ERROR(ERESTART);
                 }
-                dsl_pool_memory_pressure(dd->dd_pool);
         }
 
         if (err == 0) {
-                struct tempreserve *tr;
-
-                tr = kmem_zalloc(sizeof (struct tempreserve), KM_SLEEP);
-                tr->tr_dp = dd->dd_pool;
-                tr->tr_size = asize;
-                list_insert_tail(tr_list, tr);
-
                 err = dsl_dir_tempreserve_impl(dd, asize, fsize >= asize,
                     FALSE, asize > usize, tr_list, tx, TRUE);
         }
 
         if (err != 0)

@@ -780,14 +778,12 @@
         ASSERT3U(tx->tx_txg, !=, 0);
 
         if (tr_cookie == NULL)
                 return;
 
-        while (tr = list_head(tr_list)) {
-                if (tr->tr_dp) {
-                        dsl_pool_tempreserve_clear(tr->tr_dp, tr->tr_size, tx);
-                } else if (tr->tr_ds) {
+        while ((tr = list_head(tr_list)) != NULL) {
+                if (tr->tr_ds) {
                         mutex_enter(&tr->tr_ds->dd_lock);
                         ASSERT3U(tr->tr_ds->dd_tempreserved[txgidx], >=,
                             tr->tr_size);
                         tr->tr_ds->dd_tempreserved[txgidx] -= tr->tr_size;
                         mutex_exit(&tr->tr_ds->dd_lock);

@@ -799,12 +795,18 @@
         }
 
         kmem_free(tr_list, sizeof (list_t));
 }
 
-static void
-dsl_dir_willuse_space_impl(dsl_dir_t *dd, int64_t space, dmu_tx_t *tx)
+/*
+ * This should be called from open context when we think we're going to write
+ * or free space, for example when dirtying data. Be conservative; it's okay
+ * to write less space or free more, but we don't want to write more or free
+ * less than the amount specified.
+ */
+void
+dsl_dir_willuse_space(dsl_dir_t *dd, int64_t space, dmu_tx_t *tx)
 {
         int64_t parent_space;
         uint64_t est_used;
 
         mutex_enter(&dd->dd_lock);

@@ -818,25 +820,13 @@
         /* Make sure that we clean up dd_space_to* */
         dsl_dir_dirty(dd, tx);
 
         /* XXX this is potentially expensive and unnecessary... */
         if (parent_space && dd->dd_parent)
-                dsl_dir_willuse_space_impl(dd->dd_parent, parent_space, tx);
+                dsl_dir_willuse_space(dd->dd_parent, parent_space, tx);
 }
 
-/*
- * Call in open context when we think we're going to write/free space,
- * eg. when dirtying data.  Be conservative (ie. OK to write less than
- * this or free more than this, but don't write more or free less).
- */
-void
-dsl_dir_willuse_space(dsl_dir_t *dd, int64_t space, dmu_tx_t *tx)
-{
-        dsl_pool_willuse_space(dd->dd_pool, space, tx);
-        dsl_dir_willuse_space_impl(dd, space, tx);
-}
-
 /* call from syncing context when we actually write/free space for this dd */
 void
 dsl_dir_diduse_space(dsl_dir_t *dd, dd_used_t type,
     int64_t used, int64_t compressed, int64_t uncompressed, dmu_tx_t *tx)
 {