presto-spi/src/main/java/io/prestosql/spi/connector/FixedPageSource.java/FixedPageSource/FixedPageSource
class FixedPageSource:    public FixedPageSource(Iterable<Page> pages)
    {
        this.pages = requireNonNull(pages, "pages is null").iterator();

        long memoryUsageBytes = 0;
        for (Page page : pages) {
            memoryUsageBytes += page.getRetainedSizeInBytes();
        }
        this.memoryUsageBytes = memoryUsageBytes;
    }