perf: tighten thumbnail cache memory usage

internal/api/thumbnail_cache.go

@@ -37,7 +37,7 @@ func newThumbnailCache() *thumbnailCache {
 		items:    make(map[thumbnailCacheKey]*list.Element),
 		order:    list.New(),
 		flights:  make(map[thumbnailCacheKey]*thumbnailFlight),
-		maxBytes: 32 << 20,
+		maxBytes: 8 << 20,
 		maxItems: 64,
 	}
 }
@@ -53,7 +53,7 @@ func (c *thumbnailCache) Do(key thumbnailCacheKey, fn func() ([]byte, error)) ([
 	if f, ok := c.flights[key]; ok {
 		c.mu.Unlock()
 		<-f.done
-		return append([]byte(nil), f.data...), f.err
+		return f.data, f.err
 	}
 	f := &thumbnailFlight{done: make(chan struct{})}
 	c.flights[key] = f
@@ -63,7 +63,7 @@ func (c *thumbnailCache) Do(key thumbnailCacheKey, fn func() ([]byte, error)) ([
 	if err == nil && len(data) > 0 && int64(len(data)) <= c.maxBytes {
 		c.mu.Lock()
 		c.putLocked(key, data)
-		f.data = append([]byte(nil), data...)
+		f.data = data
 		f.err = err
 		delete(c.flights, key)
 		close(f.done)
@@ -82,11 +82,11 @@ func (c *thumbnailCache) putLocked(key thumbnailCacheKey, data []byte) {
 	if e, ok := c.items[key]; ok {
 		old := e.Value.(thumbnailCacheEntry)
 		c.bytes -= int64(len(old.data))
-		e.Value = thumbnailCacheEntry{key: key, data: append([]byte(nil), data...)}
+		e.Value = thumbnailCacheEntry{key: key, data: data}
 		c.bytes += int64(len(data))
 		c.order.MoveToFront(e)
 	} else {
-		e := c.order.PushFront(thumbnailCacheEntry{key: key, data: append([]byte(nil), data...)})
+		e := c.order.PushFront(thumbnailCacheEntry{key: key, data: data})
 		c.items[key] = e
 		c.bytes += int64(len(data))
 	}

internal/api/thumbnail_cache_test.go

@@ -70,3 +70,19 @@ func TestThumbnailCacheEvictsByBound(t *testing.T) {
 		t.Fatalf("cache size=%d/list=%d, want 2/2", len(c.items), c.order.Len())
 	}
 }
+
+func TestThumbnailCacheEvictsByBytes(t *testing.T) {
+	c := newThumbnailCache()
+	c.maxBytes = 3
+	for i := 0; i < 2; i++ {
+		key := thumbnailCacheKey{Path: string(rune('x' + i))}
+		if _, err := c.Do(key, func() ([]byte, error) { return []byte("xx"), nil }); err != nil {
+			t.Fatal(err)
+		}
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.bytes > c.maxBytes || len(c.items) != 1 {
+		t.Fatalf("cache bytes=%d items=%d, want <=%d/1", c.bytes, len(c.items), c.maxBytes)
+	}
+}