OpenZFS 9166 - zfs storage pool checkpoint

Details about the motivation of this feature and its usage can
be found in this blogpost:

    https://sdimitro.github.io/post/zpool-checkpoint/

A lightning talk of this feature can be found here:
https://www.youtube.com/watch?v=fPQA8K40jAM

Implementation details can be found in big block comment of
spa_checkpoint.c

Side-changes that are relevant to this commit but not explained
elsewhere:

* renames members of "struct metaslab trees to be shorter without
  losing meaning

* space_map_{alloc,truncate}() accept a block size as a
  parameter. The reason is that in the current state all space
  maps that we allocate through the DMU use a global tunable
  (space_map_blksz) which defauls to 4KB. This is ok for metaslab
  space maps in terms of bandwirdth since they are scattered all
  over the disk. But for other space maps this default is probably
  not what we want. Examples are device removal's vdev_obsolete_sm
  or vdev_chedkpoint_sm from this review. Both of these have a
  1:1 relationship with each vdev and could benefit from a bigger
  block size.

Porting notes:

* The part of dsl_scan_sync() which handles async destroys has
  been moved into the new dsl_process_async_destroys() function.

* Remove "VERIFY(!(flags & FWRITE))" in "kernel.c" so zhack can write
  to block device backed pools.

* ZTS:
  * Fix get_txg() in zpool_sync_001_pos due to "checkpoint_txg".

  * Don't use large dd block sizes on /dev/urandom under Linux in
    checkpoint_capacity.

  * Adopt Delphix-OS's setting of 4 (spa_asize_inflation =
    SPA_DVAS_PER_BP + 1) for the checkpoint_capacity test to speed
    its attempts to fill the pool

  * Create the base and nested pools with sync=disabled to speed up
    the "setup" phase.

  * Clear labels in test pool between checkpoint tests to avoid
    duplicate pool issues.

  * The import_rewind_device_replaced test has been marked as "known
    to fail" for the reasons listed in its DISCLAIMER.

  * New module parameters:

      zfs_spa_discard_memory_limit,
      zfs_remove_max_bytes_pause (not documented - debugging only)
      vdev_max_ms_count (formerly metaslabs_per_vdev)
      vdev_min_ms_count

Authored by: Serapheim Dimitropoulos <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: John Kennedy <[email protected]>
Reviewed by: Dan Kimmel <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Approved by: Richard Lowe <[email protected]>
Ported-by: Tim Chase <[email protected]>
Signed-off-by: Tim Chase <[email protected]>

OpenZFS-issue: https://illumos.org/issues/9166
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/7159fdb8
Closes #7570

1 files changed, 77 insertions, 5 deletions

diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index 6c7e2f55c..9410fab07 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -357,12 +357,15 @@ int spa_asize_inflation = 24;
  * These are the operations that call dsl_pool_adjustedsize() with the netfree
  * argument set to TRUE.
  *
+ * Operations that are almost guaranteed to free up space in the absence of
+ * a pool checkpoint can use up to three quarters of the slop space
+ * (e.g zfs destroy).
+ *
  * A very restricted set of operations are always permitted, regardless of
  * the amount of free space.  These are the operations that call
- * dsl_sync_task(ZFS_SPACE_CHECK_NONE), e.g. "zfs destroy".  If these
- * operations result in a net increase in the amount of space used,
- * it is possible to run the pool completely out of space, causing it to
- * be permanently read-only.
+ * dsl_sync_task(ZFS_SPACE_CHECK_NONE). If these operations result in a net
+ * increase in the amount of space used, it is possible to run the pool
+ * completely out of space, causing it to be permanently read-only.
  *
  * Note that on very small pools, the slop space will be larger than
  * 3.2%, in an effort to have it be at least spa_min_slop (128MB),
@@ -1718,6 +1721,12 @@ spa_get_dspace(spa_t *spa)
 	return (spa->spa_dspace);
 }
 
+uint64_t
+spa_get_checkpoint_space(spa_t *spa)
+{
+	return (spa->spa_checkpoint_info.sci_dspace);
+}
+
 void
 spa_update_dspace(spa_t *spa)
 {
@@ -2065,7 +2074,8 @@ spa_writeable(spa_t *spa)
 boolean_t
 spa_has_pending_synctask(spa_t *spa)
 {
-	return (!txg_all_lists_empty(&spa->spa_dsl_pool->dp_sync_tasks));
+	return (!txg_all_lists_empty(&spa->spa_dsl_pool->dp_sync_tasks) ||
+	    !txg_all_lists_empty(&spa->spa_dsl_pool->dp_early_sync_tasks));
 }
 
 int
@@ -2293,6 +2303,63 @@ spa_state_to_name(spa_t *spa)
 	return ("UNKNOWN");
 }
 
+boolean_t
+spa_top_vdevs_spacemap_addressable(spa_t *spa)
+{
+	vdev_t *rvd = spa->spa_root_vdev;
+	for (uint64_t c = 0; c < rvd->vdev_children; c++) {
+		if (!vdev_is_spacemap_addressable(rvd->vdev_child[c]))
+			return (B_FALSE);
+	}
+	return (B_TRUE);
+}
+
+boolean_t
+spa_has_checkpoint(spa_t *spa)
+{
+	return (spa->spa_checkpoint_txg != 0);
+}
+
+boolean_t
+spa_importing_readonly_checkpoint(spa_t *spa)
+{
+	return ((spa->spa_import_flags & ZFS_IMPORT_CHECKPOINT) &&
+	    spa->spa_mode == FREAD);
+}
+
+uint64_t
+spa_min_claim_txg(spa_t *spa)
+{
+	uint64_t checkpoint_txg = spa->spa_uberblock.ub_checkpoint_txg;
+
+	if (checkpoint_txg != 0)
+		return (checkpoint_txg + 1);
+
+	return (spa->spa_first_txg);
+}
+
+/*
+ * If there is a checkpoint, async destroys may consume more space from
+ * the pool instead of freeing it. In an attempt to save the pool from
+ * getting suspended when it is about to run out of space, we stop
+ * processing async destroys.
+ */
+boolean_t
+spa_suspend_async_destroy(spa_t *spa)
+{
+	dsl_pool_t *dp = spa_get_dsl(spa);
+
+	uint64_t unreserved = dsl_pool_unreserved_space(dp,
+	    ZFS_SPACE_CHECK_EXTRA_RESERVED);
+	uint64_t used = dsl_dir_phys(dp->dp_root_dir)->dd_used_bytes;
+	uint64_t avail = (unreserved > used) ? (unreserved - used) : 0;
+
+	if (spa_has_checkpoint(spa) && avail == 0)
+		return (B_TRUE);
+
+	return (B_FALSE);
+}
+
 #if defined(_KERNEL)
 
 #include <linux/mod_compat.h>
@@ -2446,6 +2513,11 @@ EXPORT_SYMBOL(spa_trust_config);
 EXPORT_SYMBOL(spa_missing_tvds_allowed);
 EXPORT_SYMBOL(spa_set_missing_tvds);
 EXPORT_SYMBOL(spa_state_to_name);
+EXPORT_SYMBOL(spa_importing_readonly_checkpoint);
+EXPORT_SYMBOL(spa_min_claim_txg);
+EXPORT_SYMBOL(spa_suspend_async_destroy);
+EXPORT_SYMBOL(spa_has_checkpoint);
+EXPORT_SYMBOL(spa_top_vdevs_spacemap_addressable);
 
 /* BEGIN CSTYLED */
 module_param(zfs_flags, uint, 0644);