diff --git a/rules/ast/ast.go b/rules/ast/ast.go
index cf720eaed..79cc768f2 100644
--- a/rules/ast/ast.go
+++ b/rules/ast/ast.go
@@ -193,7 +193,6 @@ type (
 		iterators map[clientmodel.Fingerprint]local.SeriesIterator
 		metrics   map[clientmodel.Fingerprint]clientmodel.Metric
 		// Fingerprints are populated from label matchers at query analysis time.
-		// TODO: do we still need these?
 		fingerprints clientmodel.Fingerprints
 	}
 
@@ -234,7 +233,6 @@ type (
 		iterators map[clientmodel.Fingerprint]local.SeriesIterator
 		metrics   map[clientmodel.Fingerprint]clientmodel.Metric
 		// Fingerprints are populated from label matchers at query analysis time.
-		// TODO: do we still need these?
 		fingerprints clientmodel.Fingerprints
 		interval     time.Duration
 	}
diff --git a/rules/ast/view_adapter.go b/rules/ast/view_adapter.go
deleted file mode 100644
index dc18611e8..000000000
--- a/rules/ast/view_adapter.go
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright 2013 Prometheus Team
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-// http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package ast
-
-// TODO: remove file.
diff --git a/storage/local/chunk.go b/storage/local/chunk.go
index c0f47d467..0145e2e15 100644
--- a/storage/local/chunk.go
+++ b/storage/local/chunk.go
@@ -45,9 +45,7 @@ type chunkDesc struct {
 func newChunkDesc(c chunk) *chunkDesc {
 	chunkOps.WithLabelValues(createAndPin).Inc()
 	atomic.AddInt64(&numMemChunks, 1)
-	// TODO: numMemChunkDescs is actually never read except during metrics
-	// collection. Turn it into a real metric.
-	atomic.AddInt64(&numMemChunkDescs, 1)
+	numMemChunkDescs.Inc()
 	return &chunkDesc{chunk: c, refCount: 1}
 }
 
diff --git a/storage/local/instrumentation.go b/storage/local/instrumentation.go
index 58f6125a2..9d11fbfeb 100644
--- a/storage/local/instrumentation.go
+++ b/storage/local/instrumentation.go
@@ -37,6 +37,12 @@ var (
 		},
 		[]string{opTypeLabel},
 	)
+	numMemChunkDescs = prometheus.NewGauge(prometheus.GaugeOpts{
+		Namespace: namespace,
+		Subsystem: subsystem,
+		Name:      "memory_chunkdescs",
+		Help:      "The current number of chunk descriptors in memory.",
+	})
 )
 
 const (
@@ -71,12 +77,13 @@ const (
 func init() {
 	prometheus.MustRegister(chunkOps)
 	prometheus.MustRegister(chunkDescOps)
+	prometheus.MustRegister(numMemChunkDescs)
 }
 
 var (
-	// Global counters, also used internally, so not implemented as
+	// Global counter, also used internally, so not implemented as
 	// metrics. Collected in memorySeriesStorage.Collect.
-	numMemChunks, numMemChunkDescs int64
+	numMemChunks int64
 
 	// Metric descriptors for the above.
 	numMemChunksDesc = prometheus.NewDesc(
@@ -84,9 +91,4 @@ var (
 		"The current number of chunks in memory, excluding cloned chunks (i.e. chunks without a descriptor).",
 		nil, nil,
 	)
-	numMemChunkDescsDesc = prometheus.NewDesc(
-		prometheus.BuildFQName(namespace, subsystem, "memory_chunkdescs"),
-		"The current number of chunk descriptors in memory.",
-		nil, nil,
-	)
 )
diff --git a/storage/local/persistence.go b/storage/local/persistence.go
index 513bf726b..da4ebfde2 100644
--- a/storage/local/persistence.go
+++ b/storage/local/persistence.go
@@ -766,7 +766,7 @@ func (p *persistence) loadChunkDescs(fp clientmodel.Fingerprint, beforeTime clie
 		cds = append(cds, cd)
 	}
 	chunkDescOps.WithLabelValues(load).Add(float64(len(cds)))
-	atomic.AddInt64(&numMemChunkDescs, int64(len(cds)))
+	numMemChunkDescs.Add(float64(len(cds)))
 	return cds, nil
 }
 
@@ -916,7 +916,7 @@ func (p *persistence) loadSeriesMapAndHeads() (sm *seriesMap, err error) {
 		}
 		if err == nil {
 			atomic.AddInt64(&numMemChunks, chunksTotal)
-			atomic.AddInt64(&numMemChunkDescs, chunkDescsTotal)
+			numMemChunkDescs.Add(float64(chunkDescsTotal))
 		}
 	}()
 
diff --git a/storage/local/series.go b/storage/local/series.go
index 8910cbd6f..62dc84e01 100644
--- a/storage/local/series.go
+++ b/storage/local/series.go
@@ -235,7 +235,7 @@ func (s *memorySeries) evictChunkDescs(iOldestNotEvicted int) {
 		lenEvicted := len(s.chunkDescs) - lenToKeep
 		s.chunkDescsOffset += lenEvicted
 		chunkDescOps.WithLabelValues(evict).Add(float64(lenEvicted))
-		atomic.AddInt64(&numMemChunkDescs, -int64(lenEvicted))
+		numMemChunkDescs.Sub(float64(lenEvicted))
 		s.chunkDescs = append(
 			make([]*chunkDesc, 0, lenToKeep),
 			s.chunkDescs[lenEvicted:]...,
@@ -257,7 +257,7 @@ func (s *memorySeries) purgeOlderThan(t clientmodel.Timestamp) (int, bool) {
 	}
 	if keepIdx > 0 {
 		s.chunkDescs = append(make([]*chunkDesc, 0, len(s.chunkDescs)-keepIdx), s.chunkDescs[keepIdx:]...)
-		atomic.AddInt64(&numMemChunkDescs, -int64(keepIdx))
+		numMemChunkDescs.Sub(float64(keepIdx))
 	}
 	return keepIdx, len(s.chunkDescs) == 0
 }
diff --git a/storage/local/storage.go b/storage/local/storage.go
index 20d807083..f19808eb0 100644
--- a/storage/local/storage.go
+++ b/storage/local/storage.go
@@ -801,7 +801,6 @@ func (s *memorySeriesStorage) Describe(ch chan<- *prometheus.Desc) {
 	ch <- persistQueueCapDesc
 
 	ch <- numMemChunksDesc
-	ch <- numMemChunkDescsDesc
 }
 
 // Collect implements prometheus.Collector.
@@ -820,6 +819,4 @@ func (s *memorySeriesStorage) Collect(ch chan<- prometheus.Metric) {
 
 	count := atomic.LoadInt64(&numMemChunks)
 	ch <- prometheus.MustNewConstMetric(numMemChunksDesc, prometheus.GaugeValue, float64(count))
-	count = atomic.LoadInt64(&numMemChunkDescs)
-	ch <- prometheus.MustNewConstMetric(numMemChunkDescsDesc, prometheus.GaugeValue, float64(count))
 }