Performance?: Don't unload chunks so eagerly

Previously: the Chunker tracks with chunks were gotten during the
current game tick and the N-1 and N-2 ticks, and chunks not accessed in
two ticks were freed immediately.

Now: they go into a "garbage collection" pool with a minimum number of
game ticks to free. So if they're needed again, they're saved from the
gc pool. F3 overlay data shows the count of the gc pool.

Changes.md

@@ -30,6 +30,8 @@ New levels:
 * **Swimming** (Tutorial, Lesson 5) - a tutorial level to learn how
   "water pixels" work with some moderately safe platforming puzzles
   included.
+* **Night Sky** (Azulian Tag) - a moderately difficult Azulian Tag level
+  with relatively few enemies but plenty of tricky platforming.
 * Some of the existing levels have had minor updates to take advantage
   of newer game features, such as the water being re-done for the Castle
   level.

pkg/balance/numbers.go

@@ -134,8 +134,9 @@ var (
 	EagerRenderLevelChunks = true
 
 	// Number of chunks margin outside the Canvas Viewport for the LoadingViewport.
-	LoadingViewportMarginChunks        = render.NewPoint(8, 4) // hoz, vert
+	LoadingViewportMarginChunks              = render.NewPoint(10, 8) // hoz, vert
-	CanvasLoadUnloadModuloTicks uint64 = 2
+	CanvasLoadUnloadModuloTicks       uint64 = 4
+	CanvasChunkFreeChoppingBlockTicks uint64 = 128 // number of ticks old a chunk is to free it
 )
 
 // Edit Mode Values

pkg/editor_scene.go

@@ -294,7 +294,7 @@ func (s *EditorScene) Loop(d *Doodle, ev *event.State) error {
 	}
 	if s.UI.Canvas != nil {
 		inside, outside := s.UI.Canvas.LoadUnloadMetrics()
-		*s.debLoadingViewport = fmt.Sprintf("%d in %d out %d cached", inside, outside, s.UI.Canvas.Chunker().CacheSize())
+		*s.debLoadingViewport = fmt.Sprintf("%d in %d out %d cached %d gc", inside, outside, s.UI.Canvas.Chunker().CacheSize(), s.UI.Canvas.Chunker().GCSize())
 	}
 
 	// Has the window been resized?

pkg/level/chunker.go

@@ -40,8 +40,9 @@ type Chunker struct {
 	// are actively wanted by the game.
 	lastTick              uint64 // NOTE: tracks from shmem.Tick
 	chunkRequestsThisTick map[render.Point]interface{}
-	requestsN1            map[render.Point]interface{}
+	requestsN1            map[render.Point]interface{} // chunks accessed last tick
-	requestsN2            map[render.Point]interface{}
+	requestsN2            map[render.Point]interface{} // 2 ticks ago (to free soon)
+	chunksToFree          map[render.Point]uint64      // chopping block (free after X ticks)
 	requestMu             sync.Mutex
 
 	// The palette reference from first call to Inflate()
@@ -57,6 +58,7 @@ func NewChunker(size int) *Chunker {
 		chunkRequestsThisTick: map[render.Point]interface{}{},
 		requestsN1:            map[render.Point]interface{}{},
 		requestsN2:            map[render.Point]interface{}{},
+		chunksToFree:          map[render.Point]uint64{},
 	}
 }
 
@@ -388,15 +390,25 @@ func (c *Chunker) FreeCaches() int {
 			delete_coords    = []render.Point{}
 		)
 
-		// Chunks not requested this last tick, unload from the cache.
+		// Chunks requested 2 ticks ago but not this tick, put on the chopping
+		// block to free them later.
 		for coord := range requestsN2 {
 			// Old point not requested recently?
 			if _, ok := requestsThisTick[coord]; !ok {
+				c.chunksToFree[coord] = shmem.Tick + balance.CanvasChunkFreeChoppingBlockTicks
+			}
+		}
+
+		// From the chopping block, see if scheduled chunks to free are ready.
+		for coord, expireAt := range c.chunksToFree {
+			if shmem.Tick > expireAt {
 				delete_coords = append(delete_coords, coord)
 			}
 		}
 
+		// Free any eligible chunks NOW.
 		for _, coord := range delete_coords {
+			delete(c.chunksToFree, coord)
 			c.FreeChunk(coord)
 		}
 

pkg/level/chunker_zipfile.go

@@ -82,7 +82,7 @@ func (c *Chunker) MigrateZipfile(zf *zip.Writer) error {
 					continue
 				}
 
-				log.Info("Copy existing chunk %s", file.Name)
+				log.Debug("Copy existing chunk %s", file.Name)
 				if err := zf.Copy(file); err != nil {
 					return err
 				}
@@ -105,7 +105,7 @@ func (c *Chunker) MigrateZipfile(zf *zip.Writer) error {
 		}
 
 		filename := fmt.Sprintf("chunks/%d/%s.json", c.Layer, coord.String())
-		log.Info("Flush in-memory chunks to %s", filename)
+		log.Debug("Flush in-memory chunks to %s", filename)
 		chunk.ToZipfile(zf, filename)
 	}
 
@@ -130,6 +130,11 @@ func (c *Chunker) CacheSize() int {
 	return len(c.Chunks)
 }
 
+// GCSize returns the number of chunks pending free (not accessed in 2+ ticks)
+func (c *Chunker) GCSize() int {
+	return len(c.chunksToFree)
+}
+
 // ToZipfile writes just a chunk's data into a zipfile.
 func (c *Chunk) ToZipfile(zf *zip.Writer, filename string) error {
 	writer, err := zf.Create(filename)

pkg/play_scene.go

@@ -711,7 +711,7 @@ func (s *PlayScene) Loop(d *Doodle, ev *event.State) error {
 	*s.debViewport = s.drawing.Viewport().String()
 	*s.debScroll = s.drawing.Scroll.String()
 	inside, outside := s.drawing.LoadUnloadMetrics()
-	*s.debLoadUnload = fmt.Sprintf("%d in %d out %d cached", inside, outside, s.drawing.Chunker().CacheSize())
+	*s.debLoadUnload = fmt.Sprintf("%d in %d out %d cached %d gc", inside, outside, s.drawing.Chunker().CacheSize(), s.drawing.Chunker().GCSize())
 
 	// Update the timer.
 	s.timerLabel.Text = savegame.FormatDuration(time.Since(s.startTime))