Add missing module_param for zfs_per_txg_dirty_frees_percent

When the code was added this tunable was not exposed via module params. Also it
was not documented. This patch changes the type from a uint32 to a ulong as
done with other percentage tunables and also documents it in the
zfs-module-parameters man page.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: David Quigley <david.quigley@intel.com>
Closes #5750

man/man5/zfs-module-parameters.5

@@ -1438,6 +1438,22 @@ The number of bytes which should be prefetched during a pool traversal
 Default value: \fB52,428,800\fR.
 .RE
 
+.sp
+.ne 2
+.na
+\fBzfs_per_txg_dirty_frees_percent \fR (ulong)
+.ad
+.RS 12n
+Tunable to control percentage of dirtied blocks from frees in one TXG.
+After this threshold is crossed, additional dirty blocks from frees
+wait until the next TXG.
+A value of zero will disable this throttle.
+.sp
+Default value: \fB30\fR and \fB0\fR to disable.
+.RE
+
+
+
 .sp
 .ne 2
 .na

module/zfs/dmu.c

@@ -65,7 +65,7 @@ int zfs_nopwrite_enabled = 1;
  * wait until the next TXG.
  * A value of zero will disable this throttle.
  */
-uint32_t zfs_per_txg_dirty_frees_percent = 30;
+unsigned long zfs_per_txg_dirty_frees_percent = 30;
 
 const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES] = {
 	{	DMU_BSWAP_UINT8,	TRUE,	"unallocated"		},
@@ -2228,10 +2228,15 @@ EXPORT_SYMBOL(dmu_assign_arcbuf);
 EXPORT_SYMBOL(dmu_buf_hold);
 EXPORT_SYMBOL(dmu_ot);
 
+/* BEGIN CSTYLED */
 module_param(zfs_mdcomp_disable, int, 0644);
 MODULE_PARM_DESC(zfs_mdcomp_disable, "Disable meta data compression");
 
 module_param(zfs_nopwrite_enabled, int, 0644);
 MODULE_PARM_DESC(zfs_nopwrite_enabled, "Enable NOP writes");
 
+module_param(zfs_per_txg_dirty_frees_percent, ulong, 0644);
+MODULE_PARM_DESC(zfs_per_txg_dirty_frees_percent,
+	"percentage of dirtied blocks from frees in one TXG");
+/* END CSTYLED */
 #endif