ARC statistics reset

Fixes openzfs#16437

This patch introduces a means to reset some ARC statistics without
rebooting the machine or reimporting the zfs module. Please note
that it currently only resets l2_cksum_bad and l2_io_error

Signed-off-by: Gionatan Danti <g.danti@assyoma.it>

man/man4/zfs.4

@@ -843,6 +843,10 @@ The target number of bytes the ARC should leave as free memory on the system.
 If zero, equivalent to the bigger of
 .Sy 512 KiB No and Sy all_system_memory/64 .
 .
+.It Sy zfs_arc_stats_reset Ns = Ns Sy 0 Ns | Ns 1 Pq int
+Reset ARC statistics.
+Note: it currently resets L2ARC bad checksum and error stats only.
+.
 .It Sy zfs_autoimport_disable Ns = Ns Sy 1 Ns | Ns 0 Pq int
 Disable pool import at module load by ignoring the cache file
 .Pq Sy spa_config_path .

module/zfs/arc.c

@@ -944,6 +944,9 @@ static uint64_t l2arc_trim_ahead = 0;
 static int l2arc_rebuild_enabled = B_TRUE;
 static uint64_t l2arc_rebuild_blocks_min_l2size = 1024 * 1024 * 1024;
 
+/* zfs_arc_stats_reset : reset ARC statistics */
+static int zfs_arc_stats_reset = 0;
+
 /* L2ARC persistence rebuild control routines. */
 void l2arc_rebuild_vdev(vdev_t *vd, boolean_t reopen);
 static __attribute__((noreturn)) void l2arc_dev_rebuild_thread(void *arg);
@@ -6919,6 +6922,13 @@ arc_kstat_update(kstat_t *ksp, int rw)
 	if (rw == KSTAT_WRITE)
 		return (SET_ERROR(EACCES));
 
+        /* reset ARC statistics */
+	if (zfs_arc_stats_reset) {
+		ARCSTAT_INCR(arcstat_l2_cksum_bad, -(as->arcstat_l2_cksum_bad.value.ui64));
+		ARCSTAT_INCR(arcstat_l2_io_error, -(as->arcstat_l2_io_error.value.ui64));
+		zfs_arc_stats_reset = 0;
+	}
+
 	as->arcstat_hits.value.ui64 =
 	    wmsum_value(&arc_sums.arcstat_hits);
 	as->arcstat_iohits.value.ui64 =
@@ -7166,6 +7176,19 @@ arc_kstat_update(kstat_t *ksp, int rw)
 	as->arcstat_abd_chunk_waste_size.value.ui64 =
 	    wmsum_value(&arc_sums.arcstat_abd_chunk_waste_size);
 
+	/* reset ARC statistics */
+	if (zfs_arc_stats_reset) {
+		printk (KERN_INFO "bad: %llu - sum: %llu\n", as->arcstat_l2_cksum_bad.value.ui64, wmsum_value(&arc_sums.arcstat_l2_cksum_bad));
+		ARCSTAT_INCR(arcstat_l2_cksum_bad, -(as->arcstat_l2_cksum_bad.value.ui64));
+		as->arcstat_l2_cksum_bad.value.ui64 = 0;
+		printk (KERN_INFO "nad: %llu - num: %llu\n", as->arcstat_l2_cksum_bad.value.ui64, wmsum_value(&arc_sums.arcstat_l2_cksum_bad));
+		zfs_arc_stats_reset = 0;
+		//wmsum_add(&arc_sums.arcstat_l2_cksum_bad, as->arcstat_l2_cksum_bad.value.ui64*-1);
+		//as->arcstat_l2_cksum_bad.value.ui64 = 0;
+		//as->arcstat_l2_io_error.value.ui64 = 0;
+		//wmsum_init(&arc_sums.arcstat_l2_io_error, 0);
+	}
+
 	return (0);
 }
 
@@ -10817,3 +10840,6 @@ ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, evict_batch_limit, UINT, ZMOD_RW,
 
 ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, prune_task_threads, INT, ZMOD_RW,
 	"Number of arc_prune threads");
+
+ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, stats_reset, INT, ZMOD_RW,
+	"Reset ARC statistics");