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
cffa837 code review.
A simple test case is added to the ZFS Test Suite to prevent future
regressions in functionality.

This is a backport of openzfs#9489 provided from:
openzfs#9776 (comment)

Signed-off-by: loli10K <[email protected]>

module/zfs/arc.c

@@ -296,6 +296,7 @@
 #include <sys/vmsystm.h>
 #include <sys/zpl.h>
 #include <linux/page_compat.h>
+#include <linux/mod_compat.h>
 #endif
 #include <sys/callb.h>
 #include <sys/kstat.h>
@@ -7554,8 +7555,10 @@ arc_state_multilist_index_func(multilist_t *ml, void *obj)
 
 /*
  * Called during module initialization and periodically thereafter to
- * apply reasonable changes to the exposed performance tunings.  Non-zero
- * zfs_* values which differ from the currently set values will be applied.
+ * apply reasonable changes to the exposed performance tunings.  Can also be
+ * called explicitly by param_set_arc_*() functions when ARC tunables are
+ * updated manually.  Non-zero zfs_* values which differ from the currently set
+ * values will be applied.
  */
 static void
 arc_tuning_update(void)
@@ -9389,6 +9392,35 @@ l2arc_stop(void)
 }
 
 #if defined(_KERNEL)
+static 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);
+}
+
+static 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);
+}
+
+
 EXPORT_SYMBOL(arc_buf_size);
 EXPORT_SYMBOL(arc_write);
 EXPORT_SYMBOL(arc_read);
@@ -9398,20 +9430,25 @@ EXPORT_SYMBOL(arc_add_prune_callback);
 EXPORT_SYMBOL(arc_remove_prune_callback);
 
 /* BEGIN CSTYLED */
-module_param(zfs_arc_min, ulong, 0644);
+module_param_call(zfs_arc_min, param_set_arc_long, param_get_long,
+	&zfs_arc_min, 0644);
 MODULE_PARM_DESC(zfs_arc_min, "Min arc size");
 
-module_param(zfs_arc_max, ulong, 0644);
+module_param_call(zfs_arc_max, param_set_arc_long, param_get_long,
+	&zfs_arc_max, 0644);
 MODULE_PARM_DESC(zfs_arc_max, "Max arc size");
 
-module_param(zfs_arc_meta_limit, ulong, 0644);
+module_param_call(zfs_arc_meta_limit, param_set_arc_long, param_get_long,
+	&zfs_arc_meta_limit, 0644);
 MODULE_PARM_DESC(zfs_arc_meta_limit, "Meta limit for arc size");
 
-module_param(zfs_arc_meta_limit_percent, ulong, 0644);
+module_param_call(zfs_arc_meta_limit_percent, param_set_arc_long,
+	param_get_long, &zfs_arc_meta_limit_percent, 0644);
 MODULE_PARM_DESC(zfs_arc_meta_limit_percent,
 	"Percent of arc size for arc meta limit");
 
-module_param(zfs_arc_meta_min, ulong, 0644);
+module_param_call(zfs_arc_meta_min, param_set_arc_long, param_get_long,
+	&zfs_arc_meta_min, 0644);
 MODULE_PARM_DESC(zfs_arc_meta_min, "Min arc metadata");
 
 module_param(zfs_arc_meta_prune, int, 0644);
@@ -9424,20 +9461,23 @@ MODULE_PARM_DESC(zfs_arc_meta_adjust_restarts,
 module_param(zfs_arc_meta_strategy, int, 0644);
 MODULE_PARM_DESC(zfs_arc_meta_strategy, "Meta reclaim strategy");
 
-module_param(zfs_arc_grow_retry, int, 0644);
+module_param_call(zfs_arc_grow_retry, param_set_arc_int, param_get_int,
+	&zfs_arc_grow_retry, 0644);
 MODULE_PARM_DESC(zfs_arc_grow_retry, "Seconds before growing arc size");
 
 module_param(zfs_arc_p_dampener_disable, int, 0644);
 MODULE_PARM_DESC(zfs_arc_p_dampener_disable, "disable arc_p adapt dampener");
 
-module_param(zfs_arc_shrink_shift, int, 0644);
+module_param_call(zfs_arc_shrink_shift, param_set_arc_int, param_get_int,
+	&zfs_arc_shrink_shift, 0644);
 MODULE_PARM_DESC(zfs_arc_shrink_shift, "log2(fraction of arc to reclaim)");
 
 module_param(zfs_arc_pc_percent, uint, 0644);
 MODULE_PARM_DESC(zfs_arc_pc_percent,
 	"Percent of pagecache to reclaim arc to");
 
-module_param(zfs_arc_p_min_shift, int, 0644);
+module_param_call(zfs_arc_p_min_shift, param_set_arc_int, param_get_int,
+	&zfs_arc_p_min_shift, 0644);
 MODULE_PARM_DESC(zfs_arc_p_min_shift, "arc_c shift to calc min/max arc_p");
 
 module_param(zfs_arc_average_blocksize, int, 0444);
@@ -9446,7 +9486,8 @@ MODULE_PARM_DESC(zfs_arc_average_blocksize, "Target average block size");
 module_param(zfs_compressed_arc_enabled, int, 0644);
 MODULE_PARM_DESC(zfs_compressed_arc_enabled, "Disable compressed arc buffers");
 
-module_param(zfs_arc_min_prefetch_ms, int, 0644);
+module_param_call(zfs_arc_min_prefetch_ms, param_set_arc_int, param_get_int,
+	&zfs_arc_min_prefetch_ms, 0644);
 MODULE_PARM_DESC(zfs_arc_min_prefetch_ms, "Min life of prefetch block in ms");
 
 module_param(zfs_arc_min_prescient_prefetch_ms, int, 0644);
@@ -9480,14 +9521,17 @@ MODULE_PARM_DESC(l2arc_feed_again, "Turbo L2ARC warmup");
 module_param(l2arc_norw, int, 0644);
 MODULE_PARM_DESC(l2arc_norw, "No reads during writes");
 
-module_param(zfs_arc_lotsfree_percent, int, 0644);
+module_param_call(zfs_arc_lotsfree_percent, param_set_arc_int, param_get_int,
+	&zfs_arc_lotsfree_percent, 0644);
 MODULE_PARM_DESC(zfs_arc_lotsfree_percent,
 	"System free memory I/O throttle in bytes");
 
-module_param(zfs_arc_sys_free, ulong, 0644);
+module_param_call(zfs_arc_sys_free, param_set_arc_long, param_get_long,
+	&zfs_arc_sys_free, 0644);
 MODULE_PARM_DESC(zfs_arc_sys_free, "System free memory target size in bytes");
 
-module_param(zfs_arc_dnode_limit, ulong, 0644);
+module_param_call(zfs_arc_dnode_limit, param_set_arc_long, param_get_long,
+	&zfs_arc_dnode_limit, 0644);
 MODULE_PARM_DESC(zfs_arc_dnode_limit, "Minimum bytes of dnodes in arc");
 
 module_param(zfs_arc_dnode_limit_percent, ulong, 0644);

tests/runfiles/linux.run

@@ -33,7 +33,8 @@ tests = ['alloc_class_001_pos', 'alloc_class_002_neg', 'alloc_class_003_pos',
 tags = ['functional', 'alloc_class']
 
 [tests/functional/arc]
-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]

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

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"

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