Author: mav
Date: Mon Jun  3 17:40:11 2019
New Revision: 348561
URL: https://svnweb.freebsd.org/changeset/base/348561

Log:
  MFV r348548: 9617 too-frequent TXG sync causes excessive write inflation
  
  illumos/illumos-gate@7928f4baf4ab3230557eb6289be68aa7a3003f38
  
  Reviewed by: Serapheim Dimitropoulos <serapheim.dimi...@delphix.com>
  Reviewed by: Brad Lewis <brad.le...@delphix.com>
  Reviewed by: George Wilson <george.wil...@delphix.com>
  Reviewed by: Andrew Stormont <andyjstorm...@gmail.com>
  Approved by: Robert Mustacchi <r...@joyent.com>
  Author:     Matthew Ahrens <mahr...@delphix.com>

Modified:
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h
  head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
Directory Properties:
  head/sys/cddl/contrib/opensolaris/   (props changed)

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c      Mon Jun 
 3 17:34:01 2019        (r348560)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dsl_pool.c      Mon Jun 
 3 17:40:11 2019        (r348561)
@@ -108,9 +108,11 @@ uint64_t zfs_dirty_data_max_max = 4ULL * 1024 * 1024 *
 int zfs_dirty_data_max_percent = 10;
 
 /*
- * If there is at least this much dirty data, push out a txg.
+ * If there's at least this much dirty data (as a percentage of
+ * zfs_dirty_data_max), push out a txg.  This should be less than
+ * zfs_vdev_async_write_active_min_dirty_percent.
  */
-uint64_t zfs_dirty_data_sync = 64 * 1024 * 1024;
+uint64_t zfs_dirty_data_sync_pct = 20;
 
 /*
  * Once there is this amount of dirty data, the dmu_tx_delay() will kick in
@@ -190,9 +192,9 @@ SYSCTL_PROC(_vfs_zfs, OID_AUTO, dirty_data_max_percent
     sysctl_zfs_dirty_data_max_percent, "I",
     "The percent of physical memory used to auto calculate dirty_data_max");
 
-SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, dirty_data_sync, CTLFLAG_RWTUN,
-    &zfs_dirty_data_sync, 0,
-    "Force a txg if the number of dirty buffer bytes exceed this value");
+SYSCTL_UQUAD(_vfs_zfs, OID_AUTO, dirty_data_sync_pct, CTLFLAG_RWTUN,
+    &zfs_dirty_data_sync_pct, 0,
+    "Force a txg if the percent of dirty buffer bytes exceed this value");
 
 static int sysctl_zfs_delay_min_dirty_percent(SYSCTL_HANDLER_ARGS);
 /* No zfs_delay_min_dirty_percent tunable due to limit requirements */
@@ -926,10 +928,12 @@ dsl_pool_need_dirty_delay(dsl_pool_t *dp)
 {
        uint64_t delay_min_bytes =
            zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100;
+       uint64_t dirty_min_bytes =
+           zfs_dirty_data_max * zfs_dirty_data_sync_pct / 100;
        boolean_t rv;
 
        mutex_enter(&dp->dp_lock);
-       if (dp->dp_dirty_total > zfs_dirty_data_sync)
+       if (dp->dp_dirty_total > dirty_min_bytes)
                txg_kick(dp);
        rv = (dp->dp_dirty_total > delay_min_bytes);
        mutex_exit(&dp->dp_lock);

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h  Mon Jun 
 3 17:34:01 2019        (r348560)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dsl_pool.h  Mon Jun 
 3 17:40:11 2019        (r348561)
@@ -53,7 +53,7 @@ struct dsl_scan;
 
 extern uint64_t zfs_dirty_data_max;
 extern uint64_t zfs_dirty_data_max_max;
-extern uint64_t zfs_dirty_data_sync;
+extern uint64_t zfs_dirty_data_sync_pct;
 extern int zfs_dirty_data_max_percent;
 extern int zfs_delay_min_dirty_percent;
 extern uint64_t zfs_delay_scale;

Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c
==============================================================================
--- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c   Mon Jun  3 
17:34:01 2019        (r348560)
+++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c   Mon Jun  3 
17:40:11 2019        (r348561)
@@ -490,6 +490,8 @@ txg_sync_thread(void *arg)
                uint64_t timeout = zfs_txg_timeout * hz;
                uint64_t timer;
                uint64_t txg;
+               uint64_t dirty_min_bytes =
+                   zfs_dirty_data_max * zfs_dirty_data_sync_pct / 100;
 
                /*
                 * We sync when we're scanning, there's someone waiting
@@ -501,7 +503,7 @@ txg_sync_thread(void *arg)
                    !tx->tx_exiting && timer > 0 &&
                    tx->tx_synced_txg >= tx->tx_sync_txg_waiting &&
                    !txg_has_quiesced_to_sync(dp) &&
-                   dp->dp_dirty_total < zfs_dirty_data_sync) {
+                   dp->dp_dirty_total < dirty_min_bytes) {
                        dprintf("waiting; tx_synced=%llu waiting=%llu dp=%p\n",
                            tx->tx_synced_txg, tx->tx_sync_txg_waiting, dp);
                        txg_thread_wait(tx, &cpr, &tx->tx_sync_more_cv, timer);
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