Memory Addressing

update 2017-11-15 13:22:26

View of memory:

Process 只能看到 logical pages，而 OS 则使用 physical memory maps； (not finished)

Cache

A basic design principle:

• If a correspondence is large and sparse, use a hash.
• If a correspondence is large and dense, use a cache.
• If a correspondence is small, use an array.

Influences upon memory addressing:

1. Fragmentation: the fact that allocation patterns create holes in memory space.
2. Locality: the fact that most programs access memory with localized patterns of access; the likelihood that apage access will be followed by others is high.

3. Security: the fact that processes should not be able to

   see other processes' space.

Page Tables (IA32)

A page table keeps track of the correspondence between pages and frames. Each logical address is separated into a page number and an offset;

Page table 也有可能不能完全加载，在出现page table cache miss 的时候，会发生如下：

1. interrupt the OS
2. load a new page table cache entry.
3. continue

IA64 不用 page table，而是使用 translation lookaside buffer (TLB)

In practice, this is a huge (optimized) array access: table[pgd index][pmd index][pte index]

Virtual memory

Caches, hashes, and lookasides