replace nreserved with ndirty in txgs kstat

The nreserved column in the txgs kstat file always contains 0
following the write throttle restructuring of commit
e8b96c6007bf97cdf34869c1ffbd0ce753873a3d.

Prior to that commit, the nreserved column showed the number of bytes
temporarily reserved in the pool by a transaction group at sync time.
The new write throttle did away with temporary reservations and uses
the amount of dirty data instead.  To approximate the old output of
the txgs kstat, the number of dirty bytes per-txg was passed in as
the nreserved value to spa_txg_history_set_io().  This approach did
not work as intended, because the per-txg dirty value is decremented
as data is written out to disk, so it is zero by the time we call
spa_txg_history_set_io().  To fix this, save the number of dirty
bytes before calling spa_sync(), and pass this value in to
spa_txg_history_set_io().

Also, since the name "nreserved" is now a misnomer, the column
heading is now labeled "ndirty".

Signed-off-by: Ned Bass <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Issue #1696

2 files changed, 8 insertions, 6 deletions

diff --git a/module/zfs/spa_stats.c b/module/zfs/spa_stats.c
index a35f5df65..dbc761e11 100644
--- a/module/zfs/spa_stats.c
+++ b/module/zfs/spa_stats.c
@@ -248,7 +248,7 @@ typedef struct spa_txg_history {
 	uint64_t	nwritten;	/* number of bytes written */
 	uint64_t	reads;		/* number of read operations */
 	uint64_t	writes;		/* number of write operations */
-	uint64_t	nreserved;	/* number of bytes reserved */
+	uint64_t	ndirty;		/* number of dirty bytes */
 	hrtime_t	times[TXG_STATE_COMMITTED]; /* completion times */
 	list_node_t	sth_link;
 } spa_txg_history_t;
@@ -258,7 +258,7 @@ spa_txg_history_headers(char *buf, size_t size)
 {
 	size = snprintf(buf, size - 1, "%-8s %-16s %-5s %-12s %-12s %-12s "
 	    "%-8s %-8s %-12s %-12s %-12s %-12s\n", "txg", "birth", "state",
-	    "nreserved", "nread", "nwritten", "reads", "writes",
+	    "ndirty", "nread", "nwritten", "reads", "writes",
 	    "otime", "qtime", "wtime", "stime");
 	buf[size] = '\0';
 
@@ -301,7 +301,7 @@ spa_txg_history_data(char *buf, size_t size, void *data)
 	size = snprintf(buf, size - 1, "%-8llu %-16llu %-5c %-12llu "
 	    "%-12llu %-12llu %-8llu %-8llu %-12llu %-12llu %-12llu %-12llu\n",
 	    (longlong_t)sth->txg, sth->times[TXG_STATE_BIRTH], state,
-	    (u_longlong_t)sth->nreserved,
+	    (u_longlong_t)sth->ndirty,
 	    (u_longlong_t)sth->nread, (u_longlong_t)sth->nwritten,
 	    (u_longlong_t)sth->reads, (u_longlong_t)sth->writes,
 	    (u_longlong_t)open, (u_longlong_t)quiesce, (u_longlong_t)wait,
@@ -482,7 +482,7 @@ spa_txg_history_set(spa_t *spa, uint64_t txg, txg_state_t completed_state,
  */
 int
 spa_txg_history_set_io(spa_t *spa, uint64_t txg, uint64_t nread,
-    uint64_t nwritten, uint64_t reads, uint64_t writes, uint64_t nreserved)
+    uint64_t nwritten, uint64_t reads, uint64_t writes, uint64_t ndirty)
 {
 	spa_stats_history_t *ssh = &spa->spa_stats.txg_history;
 	spa_txg_history_t *sth;
@@ -499,7 +499,7 @@ spa_txg_history_set_io(spa_t *spa, uint64_t txg, uint64_t nread,
 			sth->nwritten = nwritten;
 			sth->reads = reads;
 			sth->writes = writes;
-			sth->nreserved = nreserved;
+			sth->ndirty = ndirty;
 			error = 0;
 			break;
 		}
diff --git a/module/zfs/txg.c b/module/zfs/txg.c
index 9e9db9989..524fe8e84 100644
--- a/module/zfs/txg.c
+++ b/module/zfs/txg.c
@@ -500,6 +500,7 @@ txg_sync_thread(dsl_pool_t *dp)
 	for (;;) {
 		uint64_t timer, timeout;
 		uint64_t txg;
+		uint64_t ndirty;
 
 		timeout = zfs_txg_timeout * hz;
 
@@ -557,6 +558,7 @@ txg_sync_thread(dsl_pool_t *dp)
 
 		spa_txg_history_set(spa, txg, TXG_STATE_WAIT_FOR_SYNC,
 		    gethrtime());
+		ndirty = dp->dp_dirty_pertxg[txg & TXG_MASK];
 
 		start = ddi_get_lbolt();
 		spa_sync(spa, txg);
@@ -579,7 +581,7 @@ txg_sync_thread(dsl_pool_t *dp)
 		    vs2->vs_bytes[ZIO_TYPE_WRITE]-vs1->vs_bytes[ZIO_TYPE_WRITE],
 		    vs2->vs_ops[ZIO_TYPE_READ]-vs1->vs_ops[ZIO_TYPE_READ],
 		    vs2->vs_ops[ZIO_TYPE_WRITE]-vs1->vs_ops[ZIO_TYPE_WRITE],
-		    dp->dp_dirty_pertxg[txg & TXG_MASK]);
+		    ndirty);
 		spa_txg_history_set(spa, txg, TXG_STATE_SYNCED, gethrtime());
 	}
 }