Allow metaslab to be unloaded even when not freed from

On large systems, the memory used by loaded metaslabs can become
a concern. While range trees are a fairly efficient data structure,
on heavily fragmented pools they can still consume a significant
amount of memory. This problem is amplified when we fail to unload
metaslabs that we aren't using. Currently, we only unload a metaslab
during metaslab_sync_done; in order for that function to be called
on a given metaslab in a given txg, we have to have dirtied that
metaslab in that txg. If the dirtying was the result of an allocation,
we wouldn't be unloading it (since it wouldn't be 8 txgs since it
was selected), so in effect we only unload a metaslab during txgs
where it's being freed from.

We move the unload logic from sync_done to a new function, and
call that function on all metaslabs in a given vdev during
vdev_sync_done().

Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #8837

diff --git a/include/sys/metaslab.h b/include/sys/metaslab.h
index 2790d06c71d26327067a65e23236588994414897..330902529664ad5b13765c6257f9fe0c55e48505 100644 (file)
--- a/include/sys/metaslab.h
+++ b/include/sys/metaslab.h
@@ -50,6 +50,7 @@ int metaslab_init(metaslab_group_t *, uint64_t, uint64_t, uint64_t,
 void metaslab_fini(metaslab_t *);
 
 int metaslab_load(metaslab_t *);
+void metaslab_potentially_unload(metaslab_t *, uint64_t);
 void metaslab_unload(metaslab_t *);
 
 uint64_t metaslab_allocated_space(metaslab_t *);

diff --git a/module/zfs/metaslab.c b/module/zfs/metaslab.c
index d1d5a243f403d8be3c2fd1638bc546b78cf01c9c..41cbaad5f8dfb63d545420597b4fbeb6da9b674f 100644 (file)
--- a/module/zfs/metaslab.c
+++ b/module/zfs/metaslab.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2018 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2019 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
  * Copyright (c) 2017, Intel Corporation.
  */
@@ -2949,6 +2949,30 @@ metaslab_sync(metaslab_t *msp, uint64_t txg)
        dmu_tx_commit(tx);
 }
 
+void
+metaslab_potentially_unload(metaslab_t *msp, uint64_t txg)
+{
+       /*
+        * If the metaslab is loaded and we've not tried to load or allocate
+        * from it in 'metaslab_unload_delay' txgs, then unload it.
+        */
+       if (msp->ms_loaded &&
+           msp->ms_disabled == 0 &&
+           msp->ms_selected_txg + metaslab_unload_delay < txg) {
+               for (int t = 1; t < TXG_CONCURRENT_STATES; t++) {
+                       VERIFY0(range_tree_space(
+                           msp->ms_allocating[(txg + t) & TXG_MASK]));
+               }
+               if (msp->ms_allocator != -1) {
+                       metaslab_passivate(msp, msp->ms_weight &
+                           ~METASLAB_ACTIVE_MASK);
+               }
+
+               if (!metaslab_debug_unload)
+                       metaslab_unload(msp);
+       }
+}
+
 /*
  * Called after a transaction group has completely synced to mark
  * all of the metaslab's free space as usable.
@@ -3086,27 +3110,6 @@ metaslab_sync_done(metaslab_t *msp, uint64_t txg)
         */
        metaslab_recalculate_weight_and_sort(msp);
 
-       /*
-        * If the metaslab is loaded and we've not tried to load or allocate
-        * from it in 'metaslab_unload_delay' txgs, then unload it.
-        */
-       if (msp->ms_loaded &&
-           msp->ms_disabled == 0 &&
-           msp->ms_selected_txg + metaslab_unload_delay < txg) {
-
-               for (int t = 1; t < TXG_CONCURRENT_STATES; t++) {
-                       VERIFY0(range_tree_space(
-                           msp->ms_allocating[(txg + t) & TXG_MASK]));
-               }
-               if (msp->ms_allocator != -1) {
-                       metaslab_passivate(msp, msp->ms_weight &
-                           ~METASLAB_ACTIVE_MASK);
-               }
-
-               if (!metaslab_debug_unload)
-                       metaslab_unload(msp);
-       }
-
        ASSERT0(range_tree_space(msp->ms_allocating[txg & TXG_MASK]));
        ASSERT0(range_tree_space(msp->ms_freeing));
        ASSERT0(range_tree_space(msp->ms_freed));

diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 1c4812cd86d926888b17538fa328fa7d746ddf41..81ef87e254a82a568bf731407debaec46081d0c5 100644 (file)
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -3234,6 +3234,20 @@ vdev_sync_done(vdev_t *vd, uint64_t txg)
            != NULL)
                metaslab_sync_done(msp, txg);
 
+       /*
+        * Because this function is only called on dirty vdevs, it's possible
+        * we won't consider all metaslabs for unloading on every
+        * txg. However, unless the system is largely idle it is likely that
+        * we will dirty all vdevs within a few txgs.
+        */
+       for (int i = 0; i < vd->vdev_ms_count; i++) {
+               msp = vd->vdev_ms[i];
+               mutex_enter(&msp->ms_lock);
+               if (msp->ms_sm != NULL)
+                       metaslab_potentially_unload(msp, txg);
+               mutex_exit(&msp->ms_lock);
+       }
+
        if (reassess)
                metaslab_sync_reassess(vd->vdev_mg);
 }