[PATCH][SRU][BIONIC] UBUNTU: SAUCE: (noup) Update zfs to 0.7.5-1ubuntu16.6

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

https://bugs.launchpad.net/bugs/1772412

Sync from zfs 0.7.5-1ubuntu16.6 that contains a backport of upstream zfs
commit 77d8a0f1a4d0b2f59cee63088f7987cb38e66538 ("Fix hung z_zvol tasks
during 'zfs receive'").

Adds a dedicated, per-pool, prefetch taskq to prevent the traverse
code from monopolizing the global (and limited) system_taskq by
inappropriately scheduling long running tasks on it. This fixes
z_zvol hung tasks when performing large I/O operations, for example
when performing huge ZFS send/receives (on slow media).

Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 zfs/META                      |  2 +-
 zfs/include/sys/spa_impl.h    |  1 +
 zfs/module/zfs/dmu_traverse.c |  3 ++-
 zfs/module/zfs/spa.c          | 13 +++++++++++++
 4 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/zfs/META b/zfs/META
index 9864f8f..0823859 100644
--- a/zfs/META
+++ b/zfs/META
@@ -2,7 +2,7 @@ Meta:         1
 Name:         zfs
 Branch:       1.0
 Version:      0.7.5
-Release:      1ubuntu16.5
+Release:      1ubuntu16.6
 Release-Tags: relext
 License:      CDDL
 Author:       OpenZFS on Linux
diff --git a/zfs/include/sys/spa_impl.h b/zfs/include/sys/spa_impl.h
index 06de244..34b1199 100644
--- a/zfs/include/sys/spa_impl.h
+++ b/zfs/include/sys/spa_impl.h
@@ -275,6 +275,7 @@ struct spa {
 	spa_stats_t	spa_stats;		/* assorted spa statistics */
 	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
 	taskq_t		*spa_zvol_taskq;	/* Taskq for minor management */
+	taskq_t		*spa_prefetch_taskq;	/* Taskq for prefetch threads */
 	uint64_t	spa_multihost;		/* multihost aware (mmp) */
 	mmp_thread_t	spa_mmp;		/* multihost mmp thread */
 
diff --git a/zfs/module/zfs/dmu_traverse.c b/zfs/module/zfs/dmu_traverse.c
index 62f770e..c9171ee 100644
--- a/zfs/module/zfs/dmu_traverse.c
+++ b/zfs/module/zfs/dmu_traverse.c
@@ -31,6 +31,7 @@
 #include <sys/dsl_pool.h>
 #include <sys/dnode.h>
 #include <sys/spa.h>
+#include <sys/spa_impl.h>
 #include <sys/zio.h>
 #include <sys/dmu_impl.h>
 #include <sys/sa.h>
@@ -626,7 +627,7 @@ traverse_impl(spa_t *spa, dsl_dataset_t *ds, uint64_t objset, blkptr_t *rootbp,
 	}
 
 	if (!(flags & TRAVERSE_PREFETCH_DATA) ||
-	    taskq_dispatch(system_taskq, traverse_prefetch_thread,
+	    taskq_dispatch(spa->spa_prefetch_taskq, traverse_prefetch_thread,
 	    td, TQ_NOQUEUE) == TASKQID_INVALID)
 		pd->pd_exited = B_TRUE;
 
diff --git a/zfs/module/zfs/spa.c b/zfs/module/zfs/spa.c
index 00587d8..b777afc 100644
--- a/zfs/module/zfs/spa.c
+++ b/zfs/module/zfs/spa.c
@@ -1183,6 +1183,14 @@ spa_activate(spa_t *spa, int mode)
 	    1, INT_MAX, 0);
 
 	/*
+	 * Taskq dedicated to prefetcher threads: this is used to prevent the
+	 * pool traverse code from monopolizing the global (and limited)
+	 * system_taskq by inappropriately scheduling long running tasks on it.
+	 */
+	spa->spa_prefetch_taskq = taskq_create("z_prefetch", boot_ncpus,
+	    defclsyspri, 1, INT_MAX, TASKQ_DYNAMIC);
+
+	/*
 	 * The taskq to upgrade datasets in this pool. Currently used by
 	 * feature SPA_FEATURE_USEROBJ_ACCOUNTING.
 	 */
@@ -1211,6 +1219,11 @@ spa_deactivate(spa_t *spa)
 		spa->spa_zvol_taskq = NULL;
 	}
 
+	if (spa->spa_prefetch_taskq) {
+		taskq_destroy(spa->spa_prefetch_taskq);
+		spa->spa_prefetch_taskq = NULL;
+	}
+
 	if (spa->spa_upgrade_taskq) {
 		taskq_destroy(spa->spa_upgrade_taskq);
 		spa->spa_upgrade_taskq = NULL;
-- 
2.7.4