Fix 'zfs send/recv' hang with 16M blocks

When using 16MB blocks the send/recv queue's aren't quite big
enough.  This change leaves the default 16M queue size which a
good value for most pools.  But it additionally ensures that the
queue sizes are at least twice the allowed zfs_max_recordsize.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue openzfs#7365

man/man5/zfs-module-parameters.5

@@ -1919,6 +1919,31 @@ Allow sending of corrupt data (ignore read/checksum errors when sending data)
 Use \fB1\fR for yes and \fB0\fR for no (default).
 .RE
 
+.sp
+.ne 2
+.na
+\fBzfs_send_queue_length\fR (int)
+.ad
+.RS 12n
+The maximum number of bytes allowed in the \fBzfs send\fR queue. This value
+must be at least twice the maximum block size in use.
+.sp
+Default value: \fB16,777,216\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_recv_queue_length\fR (int)
+.ad
+.RS 12n
+.sp
+The maximum number of bytes allowed in the \fBzfs receive\fR queue. This value
+must be at least twice the maximum block size in use.
+.sp
+Default value: \fB16,777,216\fR.
+.RE
+
 .sp
 .ne 2
 .na

module/zfs/dmu_send.c

@@ -61,8 +61,8 @@
 
 /* Set this tunable to TRUE to replace corrupt data with 0x2f5baddb10c */
 int zfs_send_corrupt_data = B_FALSE;
-int zfs_send_queue_length = 16 * 1024 * 1024;
-int zfs_recv_queue_length = 16 * 1024 * 1024;
+int zfs_send_queue_length = SPA_MAXBLOCKSIZE;
+int zfs_recv_queue_length = SPA_MAXBLOCKSIZE;
 /* Set this tunable to FALSE to disable setting of DRR_FLAG_FREERECORDS */
 int zfs_send_set_freerecords_bit = B_TRUE;
 
@@ -1142,7 +1142,8 @@ dmu_send_impl(void *tag, dsl_pool_t *dp, dsl_dataset_t *to_ds,
 		goto out;
 	}
 
-	err = bqueue_init(&to_arg.q, zfs_send_queue_length,
+	err = bqueue_init(&to_arg.q,
+	    MAX(zfs_send_queue_length, 2 * zfs_max_recordsize),
 	    offsetof(struct send_block_record, ln));
 	to_arg.error_code = 0;
 	to_arg.cancel = B_FALSE;
@@ -3831,7 +3832,8 @@ dmu_recv_stream(dmu_recv_cookie_t *drc, vnode_t *vp, offset_t *voffp,
 			goto out;
 	}
 
-	(void) bqueue_init(&rwa->q, zfs_recv_queue_length,
+	(void) bqueue_init(&rwa->q,
+	    MAX(zfs_recv_queue_length, 2 * zfs_max_recordsize),
 	    offsetof(struct receive_record_arg, node));
 	cv_init(&rwa->cv, NULL, CV_DEFAULT, NULL);
 	mutex_init(&rwa->mutex, NULL, MUTEX_DEFAULT, NULL);
@@ -4242,4 +4244,10 @@ dmu_objset_is_receiving(objset_t *os)
 #if defined(_KERNEL)
 module_param(zfs_send_corrupt_data, int, 0644);
 MODULE_PARM_DESC(zfs_send_corrupt_data, "Allow sending corrupt data");
+
+module_param(zfs_send_queue_length, int, 0644);
+MODULE_PARM_DESC(zfs_send_queue_length, "Maximum send queue length");
+
+module_param(zfs_recv_queue_length, int, 0644);
+MODULE_PARM_DESC(zfs_recv_queue_length, "Maximum receive queue length");
 #endif