presto-spi/src/main/java/io/prestosql/spi/Page.java/Page/getLoadedPage
class Page:    public Page getLoadedPage()
    {
        boolean allLoaded = true;
        Block[] loadedBlocks = new Block[blocks.length];
        for (int i = 0; i < blocks.length; i++) {
            loadedBlocks[i] = blocks[i].getLoadedBlock();
            if (loadedBlocks[i] != blocks[i]) {
                allLoaded = false;
            }
        }

        if (allLoaded) {
            return this;
        }

        return new Page(loadedBlocks);
    }