CPSC 3220 - DAY 15
NOVEMBER 9, 2017

================================================================================

CHAPTER 9
---------

Cache - Copy of data that is faster than access to the original

Cache block - unit of chache storage (multiple memory locations)

Temporal locality - programs tend to reference the same memory locations
multiple times (ex instructions in a loop)

Spatial locality - programs tend to reference nearby locations (data in a loop)

Cache Concecpt (Read)

			CACHE
		 +-------------------------+
 FETCH		 |			   |	FETCH
 ADDRESS	 |	Address in 	   |	ADDRESS
---------------->|	Cache?		   |NO ------------------------->
		 |			   |
		 |			   |
		 +-------------------------+
			    YES
			     |
			     |
			STORE VALUE
			IN CACHE
			     |
			     |
			     v

Cache Concept (Write)



			CACHE
		  	 +-------------------------+
 STORE VALUE	STORE	 |			   |	FETCH
 AT ADDRESS | |	VAL@ADDR |	Address in 	   |	ADDRESS
----------->| |--------->|	Cache?		   |NO--------------------->
	    |_|	 	 |			   |
	   WRITE 	 |			   |
	   BUFFER 	 +-------------------------+
			 	    YES
			     	     |
			     	     |
				STORE VALUE
				IN CACHE
			     	     |
			     	     |			STORE VALUE
			     	     v			AT ADDRESS
				IF WRITE THROUGH --------------------------->

Hardware address translation is a powerful tool
-----------------------------------------------

Kernel trap on read/write to selected addresses
	-Copy on write
	-Fill on reference
	-Zero on use
	-Demand paged virtual memory
	-Memory mapped files
	-Modified bit emulation
	-Use bit emulation

Allocating a Page Frame
-----------------------

	-Select old page to evict
	-Find all page table entries that refer to old page
		-If page frame is shared
	-Set each page table entry to invalid
	-Remove any TLB entries
		-Copies of now invalid page table entry
	-Write changes on page back to disk, if necessary

Most machines keep dirty/use bits on page table entry

Physical page is:
	-Modified if any page table entry that points to it is modifies
	-Recently used if any page table entry that points to it if it is
	recently used