lastTrim := time.Unix(t, 0)
			if d := now.Sub(lastTrim); d < trimInterval && d > -mtimeInterval {
				return nil
			}
		}
	}

	// Trim each of the 256 subdirectories.
	// We subtract an additional mtimeInterval
	// to account for the imprecision of our "last used" mtimes.
	cutoff := now.Add(-trimLimit - mtimeInterval)
	for i := 0; i < 256; i++ {
		subdir := filepath.Join(c.dir, fmt.Sprintf("%02x", i))