Reuse more metadata buffers (#12955)

Reuse metadata buffers when no longer referenced.

Takes care of most of the happy paths.

cmd/erasure-server-pool.go

@@ -984,6 +984,7 @@ func (z *erasureServerPools) ListObjectVersions(ctx context.Context, bucket, pre
 	if err != nil && err != io.EOF {
 		return loi, err
 	}
+	defer merged.truncate(0) // Release when returning
 	if versionMarker == "" {
 		o := listPathOptions{Marker: marker}
 		// If we are not looking for a specific version skip it.
@@ -1040,6 +1041,7 @@ func (z *erasureServerPools) ListObjects(ctx context.Context, bucket, prefix, ma
 	}
 
 	merged.forwardPast(opts.Marker)
+	defer merged.truncate(0) // Release when returning
 
 	// Default is recursive, if delimiter is set then list non recursive.
 	objects := merged.fileInfos(bucket, prefix, delimiter)

cmd/metacache-entries.go

@@ -37,6 +37,9 @@ type metaCacheEntry struct {
 
 	// cached contains the metadata if decoded.
 	cached *FileInfo
+
+	// Indicates the entry can be reused and only one reference to metadata is expected.
+	reusable bool
 }
 
 // isDir returns if the entry is representing a prefix directory.
@@ -345,6 +348,8 @@ type metaCacheEntriesSorted struct {
 	o metaCacheEntries
 	// list id is not serialized
 	listID string
+	// Reuse buffers
+	reuse bool
 }
 
 // shallowClone will create a shallow clone of the array objects,
@@ -490,6 +495,15 @@ func (m *metaCacheEntriesSorted) forwardTo(s string) {
 	idx := sort.Search(len(m.o), func(i int) bool {
 		return m.o[i].name >= s
 	})
+	if m.reuse {
+		for i, entry := range m.o[:idx] {
+			if len(entry.metadata) >= metaDataReadDefault && len(entry.metadata) < metaDataReadDefault*4 {
+				metaDataPool.Put(entry.metadata)
+			}
+			m.o[i].metadata = nil
+		}
+	}
+
 	m.o = m.o[idx:]
 }
 
@@ -501,6 +515,14 @@ func (m *metaCacheEntriesSorted) forwardPast(s string) {
 	idx := sort.Search(len(m.o), func(i int) bool {
 		return m.o[i].name > s
 	})
+	if m.reuse {
+		for i, entry := range m.o[:idx] {
+			if len(entry.metadata) >= metaDataReadDefault && len(entry.metadata) < metaDataReadDefault*4 {
+				metaDataPool.Put(entry.metadata)
+			}
+			m.o[i].metadata = nil
+		}
+	}
 	m.o = m.o[idx:]
 }
 
@@ -715,6 +737,14 @@ func (m *metaCacheEntriesSorted) truncate(n int) {
 		return
 	}
 	if len(m.o) > n {
+		if m.reuse {
+			for i, entry := range m.o[n:] {
+				if len(entry.metadata) >= metaDataReadDefault && len(entry.metadata) < metaDataReadDefault*4 {
+					metaDataPool.Put(entry.metadata)
+				}
+				m.o[n+i].metadata = nil
+			}
+		}
 		m.o = m.o[:n]
 	}
 }

cmd/metacache-server-pool.go

@@ -162,6 +162,7 @@ func (z *erasureServerPools) listPath(ctx context.Context, o *listPathOptions) (
 			if o.pool < len(z.serverPools) && o.set < len(z.serverPools[o.pool].sets) {
 				o.debugln("Resuming", o)
 				entries, err = z.serverPools[o.pool].sets[o.set].streamMetadataParts(ctx, *o)
+				entries.reuse = true // We read from stream and are not sharing results.
 				if err == nil {
 					return entries, nil
 				}
@@ -217,6 +218,7 @@ func (z *erasureServerPools) listPath(ctx context.Context, o *listPathOptions) (
 	if listErr != nil && !errors.Is(listErr, context.Canceled) {
 		return entries, listErr
 	}
+	entries.reuse = true
 	truncated := entries.len() > o.Limit || err == nil
 	entries.truncate(o.Limit)
 	if !o.Transient && truncated {
@@ -363,13 +365,33 @@ func (z *erasureServerPools) listAndSave(ctx context.Context, o *listPathOptions
 		o.debugln("listAndSave: listing", o.ID, "finished with ", err)
 	}(*o)
 
+	// Keep track of when we return since we no longer have to send entries to output.
+	var funcReturned bool
+	var funcReturnedMu sync.Mutex
+	defer func() {
+		funcReturnedMu.Lock()
+		funcReturned = true
+		funcReturnedMu.Unlock()
+	}()
 	// Write listing to results and saver.
 	go func() {
+		var returned bool
 		for entry := range inCh {
-			outCh <- entry
+			if !returned {
+				funcReturnedMu.Lock()
+				returned = funcReturned
+				funcReturnedMu.Unlock()
+				outCh <- entry
+				if returned {
+					close(outCh)
+				}
+			}
+			entry.reusable = returned
 			saveCh <- entry
 		}
-		close(outCh)
+		if !returned {
+			close(outCh)
+		}
 		close(saveCh)
 	}()
 

cmd/metacache-stream.go

@@ -142,8 +142,10 @@ func (w *metacacheWriter) write(objs ...metaCacheEntry) error {
 		if err != nil {
 			return err
 		}
-		if w.reuseBlocks && cap(o.metadata) >= metaDataReadDefault {
+		if w.reuseBlocks || o.reusable {
-			metaDataPool.Put(o.metadata)
+			if cap(o.metadata) >= metaDataReadDefault && cap(o.metadata) < metaDataReadDefault*4 {
+				metaDataPool.Put(o.metadata)
+			}
 		}
 	}
 
@@ -358,10 +360,14 @@ func (r *metacacheReader) next() (metaCacheEntry, error) {
 		r.err = err
 		return m, err
 	}
-	m.metadata, err = r.mr.ReadBytes(nil)
+	m.metadata, err = r.mr.ReadBytes(metaDataPool.Get().([]byte)[:0])
 	if err == io.EOF {
 		err = io.ErrUnexpectedEOF
 	}
+	if len(m.metadata) == 0 && cap(m.metadata) >= metaDataReadDefault {
+		metaDataPool.Put(m.metadata)
+		m.metadata = nil
+	}
 	r.err = err
 	return m, err
 }
@@ -514,13 +520,17 @@ func (r *metacacheReader) readN(n int, inclDeleted, inclDirs bool, prefix string
 			r.mr.R.Skip(1)
 			return metaCacheEntriesSorted{o: res}, io.EOF
 		}
-		if meta.metadata, err = r.mr.ReadBytes(nil); err != nil {
+		if meta.metadata, err = r.mr.ReadBytes(metaDataPool.Get().([]byte)[:0]); err != nil {
 			if err == io.EOF {
 				err = io.ErrUnexpectedEOF
 			}
 			r.err = err
 			return metaCacheEntriesSorted{o: res}, err
 		}
+		if len(meta.metadata) == 0 && cap(meta.metadata) >= metaDataReadDefault {
+			metaDataPool.Put(meta.metadata)
+			meta.metadata = nil
+		}
 		if !inclDirs && meta.isDir() {
 			continue
 		}
@@ -569,13 +579,17 @@ func (r *metacacheReader) readAll(ctx context.Context, dst chan<- metaCacheEntry
 			r.err = err
 			return err
 		}
-		if meta.metadata, err = r.mr.ReadBytes(nil); err != nil {
+		if meta.metadata, err = r.mr.ReadBytes(metaDataPool.Get().([]byte)[:0]); err != nil {
 			if err == io.EOF {
 				err = io.ErrUnexpectedEOF
 			}
 			r.err = err
 			return err
 		}
+		if len(meta.metadata) == 0 && cap(meta.metadata) >= metaDataReadDefault {
+			metaDataPool.Put(meta.metadata)
+			meta.metadata = nil
+		}
 		select {
 		case <-ctx.Done():
 			r.err = ctx.Err()