kalloc.c File Reference

Kernel heap allocator implementation. More...

#include "allocator/kalloc.h"
#include "allocator/page_allocator.h"
#include "page_table/page_table.h"
#include "utils/kprintf.h"
#include "utils/string.h"
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

Include dependency graph for kalloc.c:

Data Structures
struct	allocated_block_desc_t
	Bookkeeping descriptor for a single kmalloc() allocation. More...
struct	kalloc_management_pages_t
	A page of descriptors used to track live kmalloc() allocations. More...

Macros
#define	MAX_MANAGEMENT_BLOCKS_PER_PAGE
	Number of block descriptors that fit in a single management page.

Typedefs
typedef struct allocated_block_desc_t	allocated_block_desc_t
	Bookkeeping descriptor for a single kmalloc() allocation.
typedef struct kalloc_management_pages_t	kalloc_management_pages_t
	A page of descriptors used to track live kmalloc() allocations.

Functions
static kalloc_management_pages_t *	alloc_management_page (void)
	Allocates and zero-initializes a new management page.
static allocated_block_desc_t *	find_free_management_block (void)
	Finds an unused block descriptor, growing the pool if needed.
static void	free_management_page_if_empty (allocated_block_desc_t *removed)
	Returns a management page to the page allocator once it is empty.
static void	add_to_allocated_list (allocated_block_desc_t *block)
	Appends a block descriptor to the tail of the allocated list.
static allocated_block_desc_t *	remove_from_allocated_list (void *ptr)
	Removes the descriptor for ptr from the allocated list.
void *	kmalloc (size_t size)
	Allocates a block of memory from the kernel heap.
void	kfree (void *ptr)
	Frees a block of memory previously returned by kmalloc().

Variables
static allocated_block_desc_t *	allocated = NULL
	Head of the linked list of live allocation descriptors.
static kalloc_management_pages_t *	kalloc_page_head = NULL
	Head of the linked list of management pages.

Detailed Description

Kernel heap allocator implementation.

This module implements the kernel-side dynamic memory API declared in kalloc.h. It hands out variable-sized allocations from the kernel heap and returns them for reuse, layering on top of the physical page allocator.

Author

Abhin Parekadan Jose

Date

2026-07-05

Macro Definition Documentation

MAX_MANAGEMENT_BLOCKS_PER_PAGE

#define MAX_MANAGEMENT_BLOCKS_PER_PAGE

Value:

    ((PAGE_SIZE - sizeof(struct kalloc_management_pages_t *)) / \
     sizeof(allocated_block_desc_t))

Number of block descriptors that fit in a single management page.

A management page holds an array of allocated_block_desc_t plus a pointer to the next page; this is how many descriptors fill the remaining space.

Function Documentation

add_to_allocated_list()

static void add_to_allocated_list ( allocated_block_desc_t *  block )

static

Appends a block descriptor to the tail of the allocated list.

Parameters

block

The descriptor to add. A NULL block is ignored.

alloc_management_page()

static kalloc_management_pages_t * alloc_management_page ( void  )

static

Allocates and zero-initializes a new management page.

Reserves one physical page for storing allocation descriptors and maps it to its kernel virtual address.

Returns

Pointer to the new management page, or NULL on failure.

find_free_management_block()

static allocated_block_desc_t * find_free_management_block ( void  )

static

Finds an unused block descriptor, growing the pool if needed.

Scans the existing management pages for a free descriptor and marks it used. If none are free, a new management page is allocated and appended.

Returns

Pointer to a reserved block descriptor, or NULL on failure.

free_management_page_if_empty()

static void free_management_page_if_empty ( allocated_block_desc_t *  removed )

static

Returns a management page to the page allocator once it is empty.

Locates the management page holding removed by masking the descriptor address down to its page base. If none of that page's descriptors are still in use, the page is unlinked from the management-page chain and its physical page is freed.

Parameters

removed

A descriptor that was just marked free. A NULL removed is ignored.

kfree()

void kfree

(

void *

ptr

)

Frees a block of memory previously returned by kmalloc().

Returns the block starting at ptr to the kernel heap so it can be reused. Passing NULL is a no-op.

Parameters

ptr	Pointer to the block to free, as returned by kmalloc().

kmalloc()

void * kmalloc

(

size_t

size

)

Allocates a block of memory from the kernel heap.

Reserves at least size bytes of contiguous memory for the caller.

Parameters

size	The number of bytes to allocate.

Returns

void* Pointer to the allocated block, or NULL if the request could not be satisfied.

remove_from_allocated_list()

static allocated_block_desc_t * remove_from_allocated_list ( void *  ptr )

static

Removes the descriptor for ptr from the allocated list.

Unlinks the descriptor whose allocation starts at ptr and marks it free.

Parameters

ptr	Virtual address returned by a previous kmalloc().

Returns

The removed descriptor, or NULL if ptr was not found.