Physical Memory Manager

Collaboration diagram for Physical Memory Manager:

Modules
	Internal structures and definitions
	Internal structures and definitions used by the PMM.

Data Structures
struct	page
	Represents a physical pageframe. More...

Macros
#define	PMM_INVALID_PAGEFRAME   (0xFFFFFFFFUL)
	Error value returned by the PMM in case of errors.
#define	TOTAL_PAGEFRAMES_COUNT   (ADDRESS_SPACE_SIZE / PAGE_SIZE)
	Total number of pageframes. More...
#define	TO_PFN(_pageframe)   (((native_t)(_pageframe)) >> PAGE_SHIFT)
	Convert pageframe address to page frame number.
#define	FROM_PFN(_pageframe)   ((_pageframe) << PAGE_SHIFT)
	Convert pageframe number to pageframe address.
#define	pmm_allocate()   pmm_allocate_pages(PAGE_SIZE)
	Allocate a previously unused pageframe. More...

Enumerations
enum	page_flags { PAGE_AVAILABLE = BIT(0) , PAGE_COW = BIT(1) }
	Flags used for struct page 'flags' field. More...

Functions
static paddr_t	page_address (const struct page *page)
static struct page *	pfn_to_page (unsigned int pfn)
static struct page *	address_to_page (paddr_t addr)
struct page *	page_get (struct page *page)
	Increase the page's refcount.
void	page_put (struct page *page)
	Decrease the page's refcount. More...
static bool	page_is_cow (struct page *page)
bool	pmm_init (struct multiboot_info *)
	Initialize the Physical Memory Mapper. More...
paddr_t	pmm_allocate_pages (size_t size)
	Allocate previously unused pageframes. More...
void	pmm_free_pages (paddr_t pageframe, size_t size)
	Release previously allocated contiguous pageframes.

Variables
struct page	pmm_pageframes [TOTAL_PAGEFRAMES_COUNT]
	The array of all existing pageframes. More...

Detailed Description

Physical Memory Manager

The PMM is responsible for allocating and freeing new memory pageframes. These pages are then used by the Virtual Memory Manager (e.g. UNIX's mmap) to return new (or free) mapped virtual addresses to the caller.

The PMM should never interact with the virtual address space, this is the responsabillity of the VMM only.

Design

A physical pageframe is represented by a struct page. The PMM keeps track of every existing physical page inside a statically allocated array. This array is indexed using the page's "pageframenumber". A pageframe number (PFN) is simply the page's physical address divided by the architecture's page size.

Todo:

TODO: Implement a buddy Allocator The buddy allocator is less memory efficient, but way faster when it comes to retrieving available pages.

Macro Definition Documentation

pmm_allocate

#define pmm_allocate

(

)

pmm_allocate_pages(PAGE_SIZE)

Returns

The pageframe's physical address, PMM_INVALID_PAGEFRAME on error

TOTAL_PAGEFRAMES_COUNT

#define TOTAL_PAGEFRAMES_COUNT   (ADDRESS_SPACE_SIZE / PAGE_SIZE)

This is the theorical total number of pageframes available inside the whole address space.

BUT, not all pageframes are necessarily available (usable for memory allocation). Some are reserved, used for ACPI, plus RAM is not guaranteed to be contiugous.

This constant should ONLY be used as a compile-time known theoretical reference value (e.g. the physical memory manager's bit map size).

Enumeration Type Documentation

page_flags

enum page_flags

Enumerator
PAGE_AVAILABLE	This page has not been allocated.
PAGE_COW	Currently used in a CoW mapping.

Function Documentation

address_to_page()

static struct page * address_to_page ( paddr_t  addr )

inlinestatic

Returns

The page struct corresponding to a physical address's pageframe

page_address()

static paddr_t page_address ( const struct page *  page )

inlinestatic

Returns

A page's physical address

page_is_cow()

static bool page_is_cow ( struct page *  page )

inlinestatic

Returns

whether the page is part of a CoW mapping.

page_put()

void page_put

(

struct page *

page

)

If it reaches 0, the page is released.

pfn_to_page()

static struct page * pfn_to_page ( unsigned int  pfn )

inlinestatic

Returns

The page struct corresponding to a pageframe number

pmm_allocate_pages()

paddr_t pmm_allocate_pages

(

size_t

size

)

@info The returned pageframes are guaranteed to be contiguous

Parameters

size	The size of the area to allocate (must me a multiple of PAGE_SIZE)
flags	Allocation flags

Returns

The pageframe range's physical address, PMM_INVALID_PAGEFRAME on error

pmm_init()

bool pmm_init

(

struct multiboot_info *

mbt

)

• Identify all the available page frames
• Locate the first page frame

The list of available page frames is retrieved from the memory map passed by our multiboot compliant bootloader.

Parameters

multiboot_info

The information struct passed by the multiboot-compliant bootloader to our entry function

Warning

This function should be called only once when starting the kernel. Otherwise it will overwrite the content of the underlying structures.

Variable Documentation

pmm_pageframes

struct page pmm_pageframes[TOTAL_PAGEFRAMES_COUNT]

extern

Note

The arrays's size is hardcoded to be able to fit each and every pageframes (even though only part of them will be available at runtime).

The array of all existing pageframes.

Note

The arrays's size is hardcoded to be able to fit each and every pageframes (even though only part of them will be available at runtime).