根据space ,offset 获取 buff pool的实例 下标
/******************************************************************//** Returns the buffer pool instance given space and offset of page @return buffer pool */ UNIV_INLINE buf_pool_t* buf_pool_get( /*==========*/ ulint space, /*!< in: space id */ ulint offset) /*!< in: offset of the page within space */ { ulint fold; ulint index; ulint ignored_offset; ignored_offset = offset >> ; /* 2log of BUF_READ_AHEAD_AREA (64)*/ fold = buf_page_address_fold(space, ignored_offset); index = fold % srv_buf_pool_instances; return(&buf_pool_ptr[index]); }