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 

4 files changed, 66 insertions, 1 deletions

diff --git a/tests/runfiles/linux.run b/tests/runfiles/linux.run
index 777588ac4..a134c8db8 100644
--- a/tests/runfiles/linux.run
+++ b/tests/runfiles/linux.run
@@ -25,7 +25,8 @@ tests = ['posix_001_pos', 'posix_002_pos', 'posix_003_pos']
 tags = ['functional', 'acl', 'posix']
 
 [tests/functional/arc:Linux]
-tests = ['dbufstats_001_pos', 'dbufstats_002_pos', 'dbufstats_003_pos']
+tests = ['dbufstats_001_pos', 'dbufstats_002_pos', 'dbufstats_003_pos',
+    'arcstats_runtime_tuning']
 tags = ['functional', 'arc']
 
 [tests/functional/atime:Linux]
diff --git a/tests/zfs-tests/tests/functional/arc/Makefile.am b/tests/zfs-tests/tests/functional/arc/Makefile.am
index 22704fa51..809d0346f 100644
--- a/tests/zfs-tests/tests/functional/arc/Makefile.am
+++ b/tests/zfs-tests/tests/functional/arc/Makefile.am
@@ -2,6 +2,7 @@ pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/arc
 dist_pkgdata_SCRIPTS = \
 	cleanup.ksh \
 	setup.ksh \
+	arcstats_runtime_tuning.ksh \
 	dbufstats_001_pos.ksh \
 	dbufstats_002_pos.ksh \
 	dbufstats_003_pos.ksh
diff --git a/tests/zfs-tests/tests/functional/arc/arcstats_runtime_tuning.ksh b/tests/zfs-tests/tests/functional/arc/arcstats_runtime_tuning.ksh
new file mode 100755
index 000000000..6d007aecf
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/arc/arcstats_runtime_tuning.ksh
@@ -0,0 +1,46 @@
+#!/bin/ksh -p
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright 2019, loli10K <[email protected]>. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/perf/perf.shlib
+
+function cleanup
+{
+	# Set tunables to their recorded actual size and then to their original
+	# value: this works for previously unconfigured tunables.
+	log_must set_tunable64 zfs_arc_min "$MINSIZE"
+	log_must set_tunable64 zfs_arc_min "$ZFS_ARC_MIN"
+	log_must set_tunable64 zfs_arc_max "$MAXSIZE"
+	log_must set_tunable64 zfs_arc_max "$ZFS_ARC_MAX"
+}
+
+log_onexit cleanup
+
+ZFS_ARC_MAX="$(get_tunable zfs_arc_max)"
+ZFS_ARC_MIN="$(get_tunable zfs_arc_min)"
+MINSIZE="$(get_min_arc_size)"
+MAXSIZE="$(get_max_arc_size)"
+
+log_assert "ARC tunables should be updated dynamically"
+
+for size in $((MAXSIZE/4)) $((MAXSIZE/3)) $((MAXSIZE/2)) $MAXSIZE; do
+	log_must set_tunable64 zfs_arc_max "$size"
+	log_must test "$(get_max_arc_size)" == "$size"
+	log_must set_tunable64 zfs_arc_min "$size"
+	log_must test "$(get_min_arc_size)" == "$size"
+done
+
+log_pass "ARC tunables can be updated dynamically"
diff --git a/tests/zfs-tests/tests/perf/perf.shlib b/tests/zfs-tests/tests/perf/perf.shlib
index 69e61e9fd..e2e84ca02 100644
--- a/tests/zfs-tests/tests/perf/perf.shlib
+++ b/tests/zfs-tests/tests/perf/perf.shlib
@@ -373,6 +373,23 @@ function get_directory
 	echo $directory
 }
 
+function get_min_arc_size
+{
+	if is_linux; then
+		typeset -l min_arc_size=`awk '$1 == "c_min" { print $3 }' \
+		    /proc/spl/kstat/zfs/arcstats`
+	else
+		typeset -l min_arc_size=$(dtrace -qn 'BEGIN {
+		    printf("%u\n", `arc_stats.arcstat_c_min.value.ui64);
+		    exit(0);
+		}')
+	fi
+
+	[[ $? -eq 0 ]] || log_fail "get_min_arc_size failed"
+
+	echo $min_arc_size
+}
+
 function get_max_arc_size
 {
 	if is_linux; then