pcpu_block_update
pcpu_block_update(s_block, start, e_off);
pcpu_block_update(e_block, 0, end);
pcpu_block_update(&chunk->chunk_md,
pcpu_block_update(block, s_off, e_off);
pcpu_block_update(chunk_md, bit_off, bit_off + bits);
pcpu_block_update(block, start, end);