From c1c7ce6e54560a6cfd7340d6bd6d85a5dc47798e Mon Sep 17 00:00:00 2001
From: mav <mav@FreeBSD.org>
Date: Wed, 22 Aug 2018 16:27:24 +0000
Subject: [PATCH] Create separate taskqueue to call zfs_unlinked_drain().

r334810 introduced zfs_unlinked_drain() dispatch to taskqueue on every
deletion of a file with extended attributes.  Using system_taskq for that
with its multiple threads in case of multiple files deletion caused all
available CPU threads to uselessly spin on busy locks, completely blocking
the system.

Use of single dedicated taskqueue is the only easy solution I've found,
while in would be great if we could specify that some task should be
executed only once at a time, but never in parallel, while many tasks
could use different threads same time.

Sponsored by:	iXsystems, Inc.
---
 .../contrib/opensolaris/uts/common/fs/zfs/zfs_dir.c  |  8 +++++++-
 .../opensolaris/uts/common/fs/zfs/zfs_vfsops.c       | 12 ++++++++++--
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_dir.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_dir.c
index 66a2ab590a5f..66c2713e6312 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_dir.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_dir.c
@@ -402,6 +402,10 @@ zfs_purgedir(znode_t *dzp)
 	return (skipped);
 }
 
+#if defined(__FreeBSD__)
+extern taskq_t *zfsvfs_taskq;
+#endif
+
 void
 zfs_rmnode(znode_t *zp)
 {
@@ -520,15 +524,17 @@ zfs_rmnode(znode_t *zp)
 
 	dmu_tx_commit(tx);
 
+#if defined(__FreeBSD__)
 	if (xattr_obj) {
 		/*
 		 * We're using the FreeBSD taskqueue API here instead of
 		 * the Solaris taskq API since the FreeBSD API allows for a
 		 * task to be enqueued multiple times but executed once.
 		 */
-		taskqueue_enqueue(system_taskq->tq_queue,
+		taskqueue_enqueue(zfsvfs_taskq->tq_queue,
 		    &zfsvfs->z_unlinked_drain_task);
 	}
+#endif
 }
 
 static uint64_t
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
index 66d858081485..92f51420e321 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vfsops.c
@@ -1130,6 +1130,8 @@ zfsvfs_init(zfsvfs_t *zfsvfs, objset_t *os)
 }
 
 #if defined(__FreeBSD__)
+taskq_t *zfsvfs_taskq;
+
 static void
 zfsvfs_task_unlinked_drain(void *context, int pending __unused)
 {
@@ -2185,9 +2187,9 @@ zfs_umount(vfs_t *vfsp, int fflag)
 	}
 #endif
 
-	while (taskqueue_cancel(system_taskq->tq_queue,
+	while (taskqueue_cancel(zfsvfs_taskq->tq_queue,
 	    &zfsvfs->z_unlinked_drain_task, NULL) != 0)
-		taskqueue_drain(system_taskq->tq_queue,
+		taskqueue_drain(zfsvfs_taskq->tq_queue,
 		    &zfsvfs->z_unlinked_drain_task);
 
 	VERIFY(zfsvfs_teardown(zfsvfs, B_TRUE) == 0);
@@ -2554,11 +2556,17 @@ zfs_init(void)
 	zfs_vnodes_adjust();
 
 	dmu_objset_register_type(DMU_OST_ZFS, zfs_space_delta_cb);
+#if defined(__FreeBSD__)
+	zfsvfs_taskq = taskq_create("zfsvfs", 1, minclsyspri, 0, 0, 0);
+#endif
 }
 
 void
 zfs_fini(void)
 {
+#if defined(__FreeBSD__)
+	taskq_destroy(zfsvfs_taskq);
+#endif
 	zfsctl_fini();
 	zfs_znode_fini();
 	zfs_vnodes_adjust_back();