函数buf_LRU_search_and_free_block

/******************************************************************//**
Try to free a replaceable block.
@return    TRUE if found and freed */
UNIV_INTERN
ibool
buf_LRU_search_and_free_block(
/*==========================*/
    buf_pool_t*    buf_pool,
                /*!< in: buffer pool instance */
    ulint        n_iterations)
                /*!< in: how many times this has been called
                repeatedly without result: a high value means
                that we should search farther; if
                n_iterations < 10, then we search
                n_iterations / 10 * buf_pool->curr_size
                pages from the end of the LRU list; if
                n_iterations < 5, then we will also search
                n_iterations / 5 of the unzip_LRU list. */
{
    ibool    freed = FALSE;

    buf_pool_mutex_enter(buf_pool);

    freed = buf_LRU_free_from_unzip_LRU_list(buf_pool, n_iterations); //这里    if (!freed) {
        freed = buf_LRU_free_from_common_LRU_list(buf_pool, n_iterations);//这里
    }

    if (!freed) {
        buf_pool->LRU_flush_ended = ;
    } ) {
        buf_pool->LRU_flush_ended--;
    }

    buf_pool_mutex_exit(buf_pool);

    return(freed);
}