Don't ignore zfs_arc_max below allmem/32

Set arc_c_min before arc_c_max so that when zfs_arc_min is set lower
than the default allmem/32 zfs_arc_max can also be set lower.

Add warning messages when tunables are being ignored.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Ryan Moeller <[email protected]>
Closes #10157
Closes #10158 

2 files changed, 30 insertions, 14 deletions

diff --git a/module/os/linux/zfs/arc_os.c b/module/os/linux/zfs/arc_os.c
index bff0f0517..e34d4ae08 100644
--- a/module/os/linux/zfs/arc_os.c
+++ b/module/os/linux/zfs/arc_os.c
@@ -377,7 +377,7 @@ param_set_arc_long(const char *buf, zfs_kernel_param_t *kp)
 	if (error < 0)
 		return (SET_ERROR(error));
 
-	arc_tuning_update();
+	arc_tuning_update(B_TRUE);
 
 	return (0);
 }
@@ -391,7 +391,7 @@ param_set_arc_int(const char *buf, zfs_kernel_param_t *kp)
 	if (error < 0)
 		return (SET_ERROR(error));
 
-	arc_tuning_update();
+	arc_tuning_update(B_TRUE);
 
 	return (0);
 }
diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 9c5ee9829..b5d17431c 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -4558,7 +4558,7 @@ arc_adjust_cb_check(void *arg, zthr_t *zthr)
 	 * their actual internal variable counterparts. Without this,
 	 * changing those module params at runtime would have no effect.
 	 */
-	arc_tuning_update();
+	arc_tuning_update(B_FALSE);
 
 	/*
 	 * This is necessary in order to keep the kstat information
@@ -6900,6 +6900,14 @@ arc_state_multilist_index_func(multilist_t *ml, void *obj)
 	    multilist_get_num_sublists(ml));
 }
 
+#define	WARN_IF_TUNING_IGNORED(tuning, value, do_warn) do {	\
+	if ((do_warn) && (tuning) && ((tuning) != (value))) {	\
+		cmn_err(CE_WARN,				\
+		    "ignoring tunable %s (using %llu instead)",	\
+		    (#tuning), (value));			\
+	}							\
+} while (0)
+
 /*
  * Called during module initialization and periodically thereafter to
  * apply reasonable changes to the exposed performance tunings.  Can also be
@@ -6908,11 +6916,20 @@ arc_state_multilist_index_func(multilist_t *ml, void *obj)
  * values will be applied.
  */
 void
-arc_tuning_update(void)
+arc_tuning_update(boolean_t verbose)
 {
 	uint64_t allmem = arc_all_memory();
 	unsigned long limit;
 
+	/* Valid range: 32M - <arc_c_max> */
+	if ((zfs_arc_min) && (zfs_arc_min != arc_c_min) &&
+	    (zfs_arc_min >= 2ULL << SPA_MAXBLOCKSHIFT) &&
+	    (zfs_arc_min <= arc_c_max)) {
+		arc_c_min = zfs_arc_min;
+		arc_c = MAX(arc_c, arc_c_min);
+	}
+	WARN_IF_TUNING_IGNORED(zfs_arc_min, arc_c_min, verbose);
+
 	/* Valid range: 64M - <all physical memory> */
 	if ((zfs_arc_max) && (zfs_arc_max != arc_c_max) &&
 	    (zfs_arc_max >= 64 << 20) && (zfs_arc_max < allmem) &&
@@ -6925,14 +6942,7 @@ arc_tuning_update(void)
 		if (arc_dnode_size_limit > arc_meta_limit)
 			arc_dnode_size_limit = arc_meta_limit;
 	}
-
-	/* Valid range: 32M - <arc_c_max> */
-	if ((zfs_arc_min) && (zfs_arc_min != arc_c_min) &&
-	    (zfs_arc_min >= 2ULL << SPA_MAXBLOCKSHIFT) &&
-	    (zfs_arc_min <= arc_c_max)) {
-		arc_c_min = zfs_arc_min;
-		arc_c = MAX(arc_c, arc_c_min);
-	}
+	WARN_IF_TUNING_IGNORED(zfs_arc_max, arc_c_max, verbose);
 
 	/* Valid range: 16M - <arc_c_max> */
 	if ((zfs_arc_meta_min) && (zfs_arc_meta_min != arc_meta_min) &&
@@ -6944,6 +6954,7 @@ arc_tuning_update(void)
 		if (arc_dnode_size_limit < arc_meta_min)
 			arc_dnode_size_limit = arc_meta_min;
 	}
+	WARN_IF_TUNING_IGNORED(zfs_arc_meta_min, arc_meta_min, verbose);
 
 	/* Valid range: <arc_meta_min> - <arc_c_max> */
 	limit = zfs_arc_meta_limit ? zfs_arc_meta_limit :
@@ -6952,6 +6963,7 @@ arc_tuning_update(void)
 	    (limit >= arc_meta_min) &&
 	    (limit <= arc_c_max))
 		arc_meta_limit = limit;
+	WARN_IF_TUNING_IGNORED(zfs_arc_meta_limit, arc_meta_limit, verbose);
 
 	/* Valid range: <arc_meta_min> - <arc_meta_limit> */
 	limit = zfs_arc_dnode_limit ? zfs_arc_dnode_limit :
@@ -6960,6 +6972,8 @@ arc_tuning_update(void)
 	    (limit >= arc_meta_min) &&
 	    (limit <= arc_meta_limit))
 		arc_dnode_size_limit = limit;
+	WARN_IF_TUNING_IGNORED(zfs_arc_dnode_limit, arc_dnode_size_limit,
+	    verbose);
 
 	/* Valid range: 1 - N */
 	if (zfs_arc_grow_retry)
@@ -6989,11 +7003,13 @@ arc_tuning_update(void)
 	if ((zfs_arc_lotsfree_percent >= 0) &&
 	    (zfs_arc_lotsfree_percent <= 100))
 		arc_lotsfree_percent = zfs_arc_lotsfree_percent;
+	WARN_IF_TUNING_IGNORED(zfs_arc_lotsfree_percent, arc_lotsfree_percent,
+	    verbose);
 
 	/* Valid range: 0 - <all physical memory> */
 	if ((zfs_arc_sys_free) && (zfs_arc_sys_free != arc_sys_free))
 		arc_sys_free = MIN(MAX(zfs_arc_sys_free, 0), allmem);
-
+	WARN_IF_TUNING_IGNORED(zfs_arc_sys_free, arc_sys_free, verbose);
 }
 
 static void
@@ -7183,7 +7199,7 @@ arc_init(void)
 	arc_dnode_size_limit = (percent * arc_meta_limit) / 100;
 
 	/* Apply user specified tunings */
-	arc_tuning_update();
+	arc_tuning_update(B_TRUE);
 
 	/* if kmem_flags are set, lets try to use less memory */
 	if (kmem_debugging())