update block->free after some diff data are written to the child process
update block->free after some diff data are written to the child process

JRHZRD/swapdb,JRHZRD/swapdb,JRHZRD/swapdb,JRHZRD/swapdb,JRHZRD/swapdb,JRHZRD/swapdb,JRHZRD/swapdb,JRHZRD/swapdb