Memory Management in Operating Systems: Principle, Memory Hierarchy, and Paging - Prof. B., Study notes of Operating Systems

Download Memory Management in Operating Systems: Principle, Memory Hierarchy, and Paging - Prof. B. and more Study notes Operating Systems in PDF only on Docsity! CMSC 321: Operating Systems Lecture 11 Memory Management Reading: Silberschatz Chs. 8 and 9 Memory Management? • Principle Operation: bring programs into RAM for execution • Memory Hierarchy: speed/cost vs size; volatility– . OS di d• must coor nate an manage – transparent to user Dynamic Partitioning • Partitions: vary # and length • When program brought in allocate amt needed, no more • Problems? Dynamic Partitioning • Partitions: vary # and length • When program brought in allocate amt needed, no more • Problems? external fragmentation Dynamic Partitioning Algs • How to place programs into memory? – Best-fit: find partition that results in least waste – First-fit: scan from beginning until program fits – Next-fit: scan starting from last placement • Which is best? – first-fit: simplest, best, fastest – best-fit: usually worst performer (why?) – next-fit: slightly worse than first-fit Paging Frame Main memory Mat memory Rumer i ih J 1 a a a a 4 4 & = G & z z & a a by dit ib 11 Ui 1z 1 13 {¥ 14 14 Ge Pilleea Avaiiitle Prams ifs Load Prooess A Main menwory Al AQ SEES SWS TC Z <= BoanBSe Sot u am nauwnee — (be Lowi Press if  Paging ain meMery el) Lowe Progess C ‘lak memeary A Al AQ Ad le ain Aer y AM Al Load Peopes 2 Pa ing ake Mey A A.l Aa OF) Lowel Process Sed | ba] | } J ze 3 Pracess A page table oO J x Process 6 page table | 7 @| 4 1 8 i 5 2| 9 2|_6 #| 10 | 11 Process C 4|_12 page table Process D page table 13 14 Free frame list Hierarchical: Two-Level Scheme -Kliyte rot page table ee ta he user moe to Pulls yes We WUT 4-hyle user Acres space Addr. Trans. — 2 Level Virtual Address 10 bits | 10 bits | 12 bits Frame # Offset Root page table ptr ) Page " Frame ) ’ 4-kbyte page table (contains Root page table ° (contains 1024 PTEs) 1024 PTEs) LYN Program Paging Mechanism Main Memory Page Size • Factors to consider: – 1. internal fragmentation small pages : less IF small pages : more pages/process – larger page tables – 2. secondary memory large pages : more efficient xfers – 3. effect on page fault rate l f l l kas page size increases, princip e o oca ity wea ens fewer pages available in memory (More on this later) – 4. program complexity OOP, threads reduce locality