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, 36 insertions, 5 deletions

diff --git a/include/sys/dsl_synctask.h b/include/sys/dsl_synctask.h
index 6139303c1..da6c7a40d 100644
--- a/include/sys/dsl_synctask.h
+++ b/include/sys/dsl_synctask.h
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2012, 2017 by Delphix. All rights reserved.
  */
 
 #ifndef	_SYS_DSL_SYNCTASK_H
@@ -57,14 +57,41 @@ typedef enum zfs_space_check {
 	ZFS_SPACE_CHECK_RESERVED,
 
 	/*
-	 * No space check is performed.  Only operations which we expect to
-	 * result in a net reduction in space should use this
-	 * (e.g. "zfs destroy". Setting quotas & reservations also uses
-	 * this because it needs to circumvent the quota/reservation checks).
+	 * Space check allows use of three quarters of the slop space.
+	 * If there is less than 0.8% free space, the operation will
+	 * fail.
+	 */
+	ZFS_SPACE_CHECK_EXTRA_RESERVED,
+
+	/*
+	 * In all cases "zfs destroy" is expected to result in an net
+	 * reduction of space, except one. When the pool has a
+	 * checkpoint, space freed by "zfs destroy" will not actually
+	 * free anything internally. Thus, it starts failing after
+	 * three quarters of the slop space is exceeded.
+	 */
+	ZFS_SPACE_CHECK_DESTROY = ZFS_SPACE_CHECK_EXTRA_RESERVED,
+
+	/*
+	 * A channel program can run a "zfs destroy" as part of its
+	 * script and therefore has the same space_check policy when
+	 * being evaluated.
+	 */
+	ZFS_SPACE_CHECK_ZCP_EVAL = ZFS_SPACE_CHECK_DESTROY,
+
+	/*
+	 * No space check is performed. This level of space check should
+	 * be used cautiously as operations that use it can even run when
+	 * 0.8% capacity is left for use. In this scenario, if there is a
+	 * checkpoint, async destroys are suspended and any kind of freeing
+	 * can potentially add space instead of freeing it.
 	 *
 	 * See also the comments above spa_slop_shift.
 	 */
 	ZFS_SPACE_CHECK_NONE,
+
+	ZFS_SPACE_CHECK_DISCARD_CHECKPOINT = ZFS_SPACE_CHECK_NONE,
+
 } zfs_space_check_t;
 
 typedef struct dsl_sync_task {
@@ -85,6 +112,10 @@ int dsl_sync_task(const char *, dsl_checkfunc_t *,
     dsl_syncfunc_t *, void *, int, zfs_space_check_t);
 void dsl_sync_task_nowait(struct dsl_pool *, dsl_syncfunc_t *,
     void *, int, zfs_space_check_t, dmu_tx_t *);
+int dsl_early_sync_task(const char *, dsl_checkfunc_t *,
+    dsl_syncfunc_t *, void *, int, zfs_space_check_t);
+void dsl_early_sync_task_nowait(struct dsl_pool *, dsl_syncfunc_t *,
+    void *, int, zfs_space_check_t, dmu_tx_t *);
 
 #ifdef	__cplusplus
 }