page_allocator.h File Reference

Physical page allocator for managing system memory blocks. More...

#include "mem_layout/mem_layout.h"
#include "page_table/page_table.h"
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

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Macros
#define	PHYS_ADDR_NULL   ((phy_addr)NULL)
	A null physical address value.

Functions
bool	page_allocator_add_region (phy_addr mem_start, size_t mem_size, bool check_kernel_overlap)
	Registers a new physical memory region with the allocator.
bool	page_allocator_remove_region (phy_addr mem_start)
	Removes a previously registered memory region.
void	fixup_page_allocator (void)
	Rewrites allocator bitmap pointers after the switch to high virtual addresses.
bool	reserve_page (phy_addr start, size_t num_pages)
	Reserves a specific number of contiguous pages.
phy_addr	page_alloc (size_t num_pages)
	Allocates a contiguous block of physical pages.
void	page_free (phy_addr start, size_t num_pages)
	Frees a previously allocated block of physical pages.
void	page_dump_status (void)
	Scans the bitmap and prints the status of all memory regions.

Detailed Description

Physical page allocator for managing system memory blocks.

This module handles allocation and deallocation of fixed-size 4 KiB pages, tracks page usage with a bitmap, and exposes the kernel page allocator API.

Author

Abhin Parekadan Jose

Date

2026-05-16

Function Documentation

page_alloc()

phy_addr page_alloc

(

size_t

num_pages

)

Allocates a contiguous block of physical pages.

Searches for a free span of memory large enough to hold num_pages.

Parameters

num_pages

The number of contiguous 4 KiB pages requested.

Returns

phy_addr start address of the allocated block, or PHYS_ADDR_NULL if insufficient contiguous memory exists.

page_allocator_add_region()

bool page_allocator_add_region	(	phy_addr	mem_start,
		size_t	mem_size,
		bool	check_kernel_overlap
	)

Registers a new physical memory region with the allocator.

Initializes a new memory chunk for the range starting at mem_start and spanning mem_size bytes. If check_kernel_overlap is true, the region is rejected when it overlaps the kernel image.

Parameters

mem_start	The physical address of the beginning of the region.
mem_size	Total size of the region, in bytes.
check_kernel_overlap	Whether to reject regions that overlap with the kernel image.

Returns

true if the region was added successfully, false otherwise.

page_allocator_remove_region()

bool page_allocator_remove_region

(

phy_addr

mem_start

)

Removes a previously registered memory region.

Marks the region that starts at mem_start as no longer managed by the allocator.

Parameters

mem_start

The physical base address of the region to remove.

Returns

true if the region was found and removed, false otherwise.

page_dump_status()

void page_dump_status

(

void

)

Scans the bitmap and prints the status of all memory regions.

Iterates through the managed page pool and groups contiguous pages with the same status (FREE or USED) into blocks for concise UART output.

page_free()

void page_free	(	phy_addr	start,
		size_t	num_pages
	)

Frees a previously allocated block of physical pages.

Marks the specified range of pages as available for future allocations.

Parameters

start	The physical address of the first page to free.
num_pages	The number of contiguous pages to release.

reserve_page()

bool reserve_page	(	phy_addr	start,
		size_t	num_pages
	)

Reserves a specific number of contiguous pages.

Marks the specified range of pages as reserved.

Parameters

start	The physical address of the first page to reserve.
num_pages	The number of contiguous pages to reserve.

Returns

bool True if the pages were successfully reserved, false otherwise.