Split "data_size" into "meta" and "data"

Previously, the "data_size" field in the arcstats kstat contained the
amount of cached "metadata" and "data" in the ARC. The problem is this
then made it difficult to extract out just the "metadata" size, or just
the "data" size.

To make it easier to distinguish the two values, "data_size" has been
modified to count only buffers of type ARC_BUFC_DATA, and "meta_size"
was added to count only buffers of type ARC_BUFC_METADATA. If one wants
the old "data_size" value, simply sum the new "data_size" and
"meta_size" values.

Signed-off-by: Prakash Surya <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Issue #2110

1 files changed, 24 insertions, 14 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 242d0c8c5..82b35bb62 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -308,6 +308,7 @@ typedef struct arc_stats {
 	kstat_named_t arcstat_size;
 	kstat_named_t arcstat_hdr_size;
 	kstat_named_t arcstat_data_size;
+	kstat_named_t arcstat_meta_size;
 	kstat_named_t arcstat_other_size;
 	kstat_named_t arcstat_anon_size;
 	kstat_named_t arcstat_anon_evict_data;
@@ -395,6 +396,7 @@ static arc_stats_t arc_stats = {
 	{ "size",			KSTAT_DATA_UINT64 },
 	{ "hdr_size",			KSTAT_DATA_UINT64 },
 	{ "data_size",			KSTAT_DATA_UINT64 },
+	{ "meta_size",			KSTAT_DATA_UINT64 },
 	{ "other_size",			KSTAT_DATA_UINT64 },
 	{ "anon_size",			KSTAT_DATA_UINT64 },
 	{ "anon_evict_data",		KSTAT_DATA_UINT64 },
@@ -1367,6 +1369,9 @@ arc_space_consume(uint64_t space, arc_space_type_t type)
 	case ARC_SPACE_DATA:
 		ARCSTAT_INCR(arcstat_data_size, space);
 		break;
+	case ARC_SPACE_META:
+		ARCSTAT_INCR(arcstat_meta_size, space);
+		break;
 	case ARC_SPACE_OTHER:
 		ARCSTAT_INCR(arcstat_other_size, space);
 		break;
@@ -1378,7 +1383,9 @@ arc_space_consume(uint64_t space, arc_space_type_t type)
 		break;
 	}
 
-	ARCSTAT_INCR(arcstat_meta_used, space);
+	if (type != ARC_SPACE_DATA)
+		ARCSTAT_INCR(arcstat_meta_used, space);
+
 	atomic_add_64(&arc_size, space);
 }
 
@@ -1393,6 +1400,9 @@ arc_space_return(uint64_t space, arc_space_type_t type)
 	case ARC_SPACE_DATA:
 		ARCSTAT_INCR(arcstat_data_size, -space);
 		break;
+	case ARC_SPACE_META:
+		ARCSTAT_INCR(arcstat_meta_size, -space);
+		break;
 	case ARC_SPACE_OTHER:
 		ARCSTAT_INCR(arcstat_other_size, -space);
 		break;
@@ -1404,10 +1414,13 @@ arc_space_return(uint64_t space, arc_space_type_t type)
 		break;
 	}
 
-	ASSERT(arc_meta_used >= space);
-	if (arc_meta_max < arc_meta_used)
-		arc_meta_max = arc_meta_used;
-	ARCSTAT_INCR(arcstat_meta_used, -space);
+	if (type != ARC_SPACE_DATA) {
+		ASSERT(arc_meta_used >= space);
+		if (arc_meta_max < arc_meta_used)
+			arc_meta_max = arc_meta_used;
+		ARCSTAT_INCR(arcstat_meta_used, -space);
+	}
+
 	ASSERT(arc_size >= space);
 	atomic_add_64(&arc_size, -space);
 }
@@ -1604,12 +1617,11 @@ arc_buf_destroy(arc_buf_t *buf, boolean_t recycle, boolean_t all)
 		if (!recycle) {
 			if (type == ARC_BUFC_METADATA) {
 				arc_buf_data_free(buf, zio_buf_free);
-				arc_space_return(size, ARC_SPACE_DATA);
+				arc_space_return(size, ARC_SPACE_META);
 			} else {
 				ASSERT(type == ARC_BUFC_DATA);
 				arc_buf_data_free(buf, zio_data_buf_free);
-				ARCSTAT_INCR(arcstat_data_size, -size);
-				atomic_add_64(&arc_size, -size);
+				arc_space_return(size, ARC_SPACE_DATA);
 			}
 		}
 		if (list_link_active(&buf->b_hdr->b_arc_node)) {
@@ -2759,12 +2771,11 @@ arc_get_data_buf(arc_buf_t *buf)
 	if (!arc_evict_needed(type)) {
 		if (type == ARC_BUFC_METADATA) {
 			buf->b_data = zio_buf_alloc(size);
-			arc_space_consume(size, ARC_SPACE_DATA);
+			arc_space_consume(size, ARC_SPACE_META);
 		} else {
 			ASSERT(type == ARC_BUFC_DATA);
 			buf->b_data = zio_data_buf_alloc(size);
-			ARCSTAT_INCR(arcstat_data_size, size);
-			atomic_add_64(&arc_size, size);
+			arc_space_consume(size, ARC_SPACE_DATA);
 		}
 		goto out;
 	}
@@ -2809,7 +2820,7 @@ arc_get_data_buf(arc_buf_t *buf)
 	if ((buf->b_data = arc_evict(state, 0, size, recycle, evict)) == NULL) {
 		if (type == ARC_BUFC_METADATA) {
 			buf->b_data = zio_buf_alloc(size);
-			arc_space_consume(size, ARC_SPACE_DATA);
+			arc_space_consume(size, ARC_SPACE_META);
 
 			/*
 			 * If we are unable to recycle an existing meta buffer
@@ -2824,8 +2835,7 @@ arc_get_data_buf(arc_buf_t *buf)
 		} else {
 			ASSERT(type == ARC_BUFC_DATA);
 			buf->b_data = zio_data_buf_alloc(size);
-			ARCSTAT_INCR(arcstat_data_size, size);
-			atomic_add_64(&arc_size, size);
+			arc_space_consume(size, ARC_SPACE_DATA);
 		}
 
 		/* Only bump this if we tried to recycle and failed */