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 <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: loli10K <[email protected]>
Closes #9487  
Closes #9489 

1 files changed, 28 insertions, 0 deletions

diff --git a/module/os/linux/zfs/arc_os.c b/module/os/linux/zfs/arc_os.c
index 696f671ab..c9db31096 100644
--- a/module/os/linux/zfs/arc_os.c
+++ b/module/os/linux/zfs/arc_os.c
@@ -357,6 +357,34 @@ arc_lowmem_fini(void)
 {
 	spl_unregister_shrinker(&arc_shrinker);
 }
+
+int
+param_set_arc_long(const char *buf, zfs_kernel_param_t *kp)
+{
+	int error;
+
+	error = param_set_long(buf, kp);
+	if (error < 0)
+		return (SET_ERROR(error));
+
+	arc_tuning_update();
+
+	return (0);
+}
+
+int
+param_set_arc_int(const char *buf, zfs_kernel_param_t *kp)
+{
+	int error;
+
+	error = param_set_int(buf, kp);
+	if (error < 0)
+		return (SET_ERROR(error));
+
+	arc_tuning_update();
+
+	return (0);
+}
 #else /* _KERNEL */
 int64_t
 arc_available_memory(void)