函数buf_LRU_free_from_common_LRU_list

/******************************************************************//**
Try to free a clean page from the common LRU list.
@return    TRUE if freed */
UNIV_INLINE
ibool
buf_LRU_free_from_common_LRU_list(
/*==============================*/
    buf_pool_t*    buf_pool,
    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 */
{
    buf_page_t*    bpage;
    ulint        distance;

    ut_ad(buf_pool_mutex_own(buf_pool));

    distance =  + (n_iterations * buf_pool->curr_size) / ;

    for (bpage = UT_LIST_GET_LAST(buf_pool->LRU);
         UNIV_LIKELY(bpage != NULL) && UNIV_LIKELY(distance > );
         bpage = UT_LIST_GET_PREV(LRU, bpage), distance--) {

        ibool        freed;
        unsigned    accessed;
        mutex_t*    block_mutex = buf_page_get_mutex(bpage);

        ut_ad(buf_page_in_file(bpage));
        ut_ad(bpage->in_LRU_list);

        mutex_enter(block_mutex);
        accessed = buf_page_is_accessed(bpage);
        freed = buf_LRU_free_block(bpage, TRUE);
        mutex_exit(block_mutex);

        if (freed) {
            /* Keep track of pages that are evicted without
            ever being accessed. This gives us a measure of
            the effectiveness of readahead */
            if (!accessed) {
                ++buf_pool->stat.n_ra_pages_evicted;
            }
            return(TRUE);
        }
    }

    return(FALSE);
}