Fix for ARC sysctls ignored at runtime

This change leverage module_param_call() to run arc_tuning_update()
immediately after the ARC tunable has been updated as suggested in
cffa8372 code review.

A simple test case is added to the ZFS Test Suite to prevent future
regressions in functionality.

Reviewed-by: Matt Macy <mmacy@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #9487  
Closes #9489

include/os/linux/kernel/linux/mod_compat.h

@@ -76,26 +76,26 @@ enum scope_prefix_types {
 /*
  * Declare a module parameter / sysctl node
  *
- * scope_prefix the part of the the sysctl / sysfs tree the node resides under
+ * "scope_prefix" the part of the the sysctl / sysfs tree the node resides under
  *   (currently a no-op on Linux)
- * name_prefix the part of the variable name that will be excluded from the
+ * "name_prefix" the part of the variable name that will be excluded from the
  *   exported names on platforms with a hierarchical namespace
- * name the part of the variable that will be exposed on platforms with a
+ * "name" the part of the variable that will be exposed on platforms with a
  *    hierarchical namespace, or as name_prefix ## name on Linux
- * type the variable type
- * perm the permissions (read/write or read only)
- * desc a brief description of the option
+ * "type" the variable type
+ * "perm" the permissions (read/write or read only)
+ * "desc" a brief description of the option
  *
  * Examples:
  * ZFS_MODULE_PARAM(zfs_vdev_mirror, zfs_vdev_mirror_, rotating_inc, UINT,
- *	 ZMOD_RW, "Rotating media load increment for non-seeking I/O's");
+ * 	ZMOD_RW, "Rotating media load increment for non-seeking I/O's");
  * on FreeBSD:
  *   vfs.zfs.vdev.mirror.rotating_inc
  * on Linux:
  *   zfs_vdev_mirror_rotating_inc
  *
- * *ZFS_MODULE_PARAM(zfs, , dmu_prefetch_max, UINT, ZMOD_RW,
- *	"Limit one prefetch call to this size");
+ * ZFS_MODULE_PARAM(zfs, , dmu_prefetch_max, UINT, ZMOD_RW,
+ * 	"Limit one prefetch call to this size");
  * on FreeBSD:
  *   vfs.zfs.dmu_prefetch_max
  * on Linux:
@@ -108,5 +108,33 @@ enum scope_prefix_types {
 	MODULE_PARM_DESC(name_prefix ## name, desc)
 /* END CSTYLED */
 
+/*
+ * Declare a module parameter / sysctl node
+ *
+ * "scope_prefix" the part of the the sysctl / sysfs tree the node resides under
+ *   (currently a no-op on Linux)
+ * "name_prefix" the part of the variable name that will be excluded from the
+ *   exported names on platforms with a hierarchical namespace
+ * "name" the part of the variable that will be exposed on platforms with a
+ *    hierarchical namespace, or as name_prefix ## name on Linux
+ * "setfunc" setter function
+ * "getfunc" getter function
+ * "perm" the permissions (read/write or read only)
+ * "desc" a brief description of the option
+ *
+ * Examples:
+ * ZFS_MODULE_PARAM_CALL(zfs_spa, spa_, slop_shift, param_set_slop_shift,
+ * 	param_get_int, ZMOD_RW, "Reserved free space in pool");
+ * on FreeBSD:
+ *   vfs.zfs.spa_slop_shift
+ * on Linux:
+ *   spa_slop_shift
+ */
+/* BEGIN CSTYLED */
+#define ZFS_MODULE_PARAM_CALL(scope_prefix, name_prefix, name, setfunc, getfunc, perm, desc) \
+	CTASSERT_GLOBAL((sizeof (scope_prefix) == sizeof (enum scope_prefix_types))); \
+	module_param_call(name_prefix ## name, setfunc, getfunc, &name_prefix ## name, perm); \
+	MODULE_PARM_DESC(name_prefix ## name, desc)
+/* END CSTYLED */
 
 #endif	/* _MOD_COMPAT_H */

include/sys/arc_impl.h

@@ -611,6 +611,10 @@ extern void arc_prune_async(int64_t);
 extern int arc_memory_throttle(spa_t *spa, uint64_t reserve, uint64_t txg);
 extern uint64_t arc_free_memory(void);
 extern int64_t arc_available_memory(void);
+extern void arc_tuning_update(void);
+
+extern int param_set_arc_long(const char *buf, zfs_kernel_param_t *kp);
+extern int param_set_arc_int(const char *buf, zfs_kernel_param_t *kp);
 
 #ifdef __cplusplus
 }

include/sys/zfs_context.h

@@ -198,7 +198,13 @@ extern int aok;
 /*
  * Tunables.
  */
+typedef struct zfs_kernel_param {
+	const char *name;	/* unused stub */
+} zfs_kernel_param_t;
+
 #define	ZFS_MODULE_PARAM(scope_prefix, name_prefix, name, type, perm, desc)
+#define	ZFS_MODULE_PARAM_CALL(scope_prefix, name_prefix, name, setfunc, \
+	getfunc, perm, desc)
 
 /*
  * Exported symbols