[Stormdos-develop] 22 dec 2004 - new memory management doc. - "memdoc.txt"

[Juras <yb...@tu...>]

Hello stormdos-develop,

Memory management in SD-32-C2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Designed by Yury Benesh
22 December, 2004


Virtual memory addressing is used where each process uses 4 GiB address
space which doesn't correspond to equal physical addresses.

A part of PAGE DIRECTORY describing PAGE TABLES for the first 2 GiB
are copied among all address spaces/processes/applications.

Next 2 GiBs are private to all processes. While the first 1 GiB of it
is for application addresses ( EXEcutable image, heap, dynamic memory etc. )
and higher 1 GiB is for DLLs.

Memory addresses are controled via linked lists which can occupy more
memory when the allocated block is insufficient for adding new
free memory region structure.

A memory block is allocated and measured by 4 KiB pages.

There's one global linked list for describing lowest 2 GiB ( also called
system/kernel memory region ) - through these addresses all system
structures and page tables are accessed. It is also can be used
by drivers.

There is a linked lists for each process/application to control
its private memory region.

There is also one global linked list to control free addresses in
the upper memory for DLLs.

The hierarchy:

THE LOWEST LAYER OF THE MEMORY MANAGER
--------------------------------------

- get physical page ( DOS, DMA, HIGH, ANY )
- fill the page directory
- reserve pages
( bit 11 of table entries is used to mark non-present but reserved pages )
- alloc table
- add/remove free blocks
( adds memory addresses to the global list of free 0..2 GiB addresses )
- set pages addr, flags


THE MIDDLE/DRIVER LAYER
-----------------------

- allocate/free ( DOS, DMA, HIGH, ANY) block of pages - returns ready virtual
address

- reserve tables and/or directory entries in the range of the kernel
memory region for storing page tables in adjacent addresses
 ( removes addresses from the global list of free 0..2 GiB addresses )

- map physical page to linear ( involves allocation of physical pages
for the reserved tables if needed )



THE TOP/APP LAYER
-----------------

- allocate/free heap ( in 4 KiB )
- allocate/free block of bytes in the heap  

-- 
Best regards,
 Juras                          mailto:yb...@tu...