Restore FreeBSD sysctl processing for arc.min and arc.max

Before OpenZFS 2.0, trying to set the FreeBSD sysctl vfs.zfs.arc_max
to a disallowed value would return an error.
Since the switch, it instead only generates WARN_IF_TUNING_IGNORED

Also lost, was the ability to set vfs.zfs.arc_max to a value less
than the default vfs.zfs.arc_min at boot time. Restore this as well.

Signed-off-by: Allan Jude <allan@klarasystems.com>

include/os/freebsd/spl/sys/mod_os.h

@@ -62,6 +62,12 @@
 #define	param_set_arc_long_args(var) \
     CTLTYPE_ULONG, &var, 0, param_set_arc_long, "LU"
 
+#define	param_set_arc_min_args(var) \
+    CTLTYPE_ULONG, &var, 0, param_set_arc_min, "LU"
+
+#define	param_set_arc_max_args(var) \
+    CTLTYPE_ULONG, &var, 0, param_set_arc_max, "LU"
+
 #define	param_set_arc_int_args(var) \
     CTLTYPE_INT, &var, 0, param_set_arc_int, "I"
 

include/sys/arc_impl.h

@@ -932,6 +932,8 @@ extern void arc_unregister_hotplug(void);
 
 extern int param_set_arc_long(ZFS_MODULE_PARAM_ARGS);
 extern int param_set_arc_int(ZFS_MODULE_PARAM_ARGS);
+extern int param_set_arc_min(ZFS_MODULE_PARAM_ARGS);
+extern int param_set_arc_max(ZFS_MODULE_PARAM_ARGS);
 
 /* used in zdb.c */
 boolean_t l2arc_log_blkptr_valid(l2arc_dev_t *dev,

module/os/freebsd/zfs/sysctl_os.c

@@ -144,6 +144,52 @@ extern arc_state_t ARC_l2c_only;
 
 /* arc.c */
 
+int
+param_set_arc_max(SYSCTL_HANDLER_ARGS)
+{
+	uint64_t val;
+	int err;
+
+	val = zfs_arc_max;
+	err = sysctl_handle_long(oidp, &val, 0, req);
+	if (err != 0 || req->newptr == NULL)
+		return (SET_ERROR(err));
+
+	if (val < 64 << 20 || val <= arc_c_min || val >= arc_all_memory())
+		return (SET_ERROR(EINVAL));
+
+	zfs_arc_max = val;
+	arc_tuning_update(B_TRUE);
+
+	/* Update the sysctl to the tuned value */
+	zfs_arc_max = arc_c_max;
+
+	return (0);
+}
+
+int
+param_set_arc_min(SYSCTL_HANDLER_ARGS)
+{
+	uint64_t val;
+	int err;
+
+	val = zfs_arc_min;
+	err = sysctl_handle_64(oidp, &val, 0, req);
+	if (err != 0 || req->newptr == NULL)
+		return (SET_ERROR(err));
+
+	if (val < 2ULL << SPA_MAXBLOCKSHIFT || val > arc_c_max)
+		return (SET_ERROR(EINVAL));
+
+	zfs_arc_min = val;
+	arc_tuning_update(B_TRUE);
+
+	/* Update the sysctl to the tuned value */
+	zfs_arc_min = arc_c_min;
+
+	return (0);
+}
+
 /* legacy compat */
 extern uint64_t l2arc_write_max;	/* def max write size */
 extern uint64_t l2arc_write_boost;	/* extra warmup write */
@@ -278,11 +324,11 @@ param_set_arc_int(SYSCTL_HANDLER_ARGS)
 
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_min,
     CTLTYPE_ULONG | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-    &zfs_arc_min, sizeof (zfs_arc_min), param_set_arc_long, "LU",
+    &zfs_arc_min, sizeof (zfs_arc_min), param_set_arc_min, "LU",
     "min arc size (LEGACY)");
 SYSCTL_PROC(_vfs_zfs, OID_AUTO, arc_max,
     CTLTYPE_ULONG | CTLFLAG_RWTUN | CTLFLAG_MPSAFE,
-    &zfs_arc_max, sizeof (zfs_arc_max), param_set_arc_long, "LU",
+    &zfs_arc_max, sizeof (zfs_arc_max), param_set_arc_max, "LU",
     "max arc size (LEGACY)");
 
 /* dbuf.c */

module/os/linux/zfs/arc_os.c

@@ -371,6 +371,18 @@ param_set_arc_long(const char *buf, zfs_kernel_param_t *kp)
 	return (0);
 }
 
+int
+param_set_arc_min(const char *buf, zfs_kernel_param_t *kp)
+{
+	return (param_set_arc_long(buf, kp));
+}
+
+int
+param_set_arc_max(const char *buf, zfs_kernel_param_t *kp)
+{
+	return (param_set_arc_long(buf, kp));
+}
+
 int
 param_set_arc_int(const char *buf, zfs_kernel_param_t *kp)
 {

module/zfs/arc.c

@@ -7618,7 +7618,23 @@ arc_init(void)
 
 	arc_set_limits(allmem);
 
-#ifndef _KERNEL
+#ifdef _KERNEL
+	/*
+	 * If zfs_arc_max is non-zero at init, meaning it was set in the kernel
+	 * environment before the module was loaded, don't block setting the
+	 * maximum because it is less than arc_c_min, instead, reset arc_c_min
+	 * to a lower value.
+	 * zfs_arc_min will be handled by arc_tuning_update().
+	 */
+	if (zfs_arc_max != 0 && zfs_arc_max > 64 << 20 &&
+	    zfs_arc_max < allmem) {
+		arc_c_max = zfs_arc_max;
+		if (arc_c_min >= arc_c_max) {
+			arc_c_min = MAX(zfs_arc_max / 2,
+			    2ULL << SPA_MAXBLOCKSHIFT);
+		}
+	}
+#else
 	/*
 	 * In userland, there's only the memory pressure that we artificially
 	 * create (see arc_available_memory()).  Don't let arc_c get too
@@ -10651,10 +10667,10 @@ EXPORT_SYMBOL(arc_add_prune_callback);
 EXPORT_SYMBOL(arc_remove_prune_callback);
 
 /* BEGIN CSTYLED */
-ZFS_MODULE_PARAM_CALL(zfs_arc, zfs_arc_, min, param_set_arc_long,
+ZFS_MODULE_PARAM_CALL(zfs_arc, zfs_arc_, min, param_set_arc_min,
 	param_get_long, ZMOD_RW, "Min arc size");
 
-ZFS_MODULE_PARAM_CALL(zfs_arc, zfs_arc_, max, param_set_arc_long,
+ZFS_MODULE_PARAM_CALL(zfs_arc, zfs_arc_, max, param_set_arc_max,
 	param_get_long, ZMOD_RW, "Max arc size");
 
 ZFS_MODULE_PARAM_CALL(zfs_arc, zfs_arc_, meta_limit, param_set_arc_long,