Memory slab allocator implementation in kernel. This file provides functions for managing memory allocation using the slab allocator technique. Slab allocators are efficient in managing frequent small memory allocations with minimal fragmentation. More...

Classes
struct	kmem_obj
	Structure to represent an individual memory object within a slab. More...

Macros
#define	__DEBUG_HEADER__ "[SLAB ]"
	Change header.

#define	__DEBUG_LEVEL__ LOGLEVEL_NOTICE
	Set log level.

#define	MAX_KMALLOC_CACHE_ORDER 12
	Maximum order of kmalloc cache allocations. More...

#define	KMEM_OBJ_OVERHEAD sizeof(kmem_obj_t)
	Overhead size for each memory object in the slab cache. More...

#define	KMEM_START_OBJ_COUNT 8
	Initial object count for each slab. More...

#define	KMEM_MAX_REFILL_OBJ_COUNT 64
	Maximum number of objects to refill in a slab cache at once. More...

#define	KMEM_OBJ_FROM_ADDR(addr) ((kmem_obj_t *)(addr))
	Macro to convert an address into a kmem_obj pointer. More...

#define	ADDR_FROM_KMEM_OBJ(object) ((void *)(object))
	Macro to get the address from a kmem_obj structure. More...

Typedefs
typedef struct kmem_obj	kmem_obj_t
	Structure to represent an individual memory object within a slab. More...

Functions
static int	__alloc_slab_page (kmem_cache_t *cachep, gfp_t flags)
	Allocates and initializes a new slab page for a memory cache. More...

static int	__kmem_cache_refill (kmem_cache_t *cachep, unsigned int free_num, gfp_t flags)
	Refills a memory cache with new slab pages to reach a specified number of free objects. More...

static int	__compute_size_and_order (kmem_cache_t *cachep)
	Computes and sets the size and gfp order for a memory cache. More...

static int	__kmem_cache_create (kmem_cache_t cachep, const char name, unsigned int size, unsigned int align, slab_flags_t flags, kmem_fun_t ctor, kmem_fun_t dtor, unsigned int start_count)
	Initializes and creates a new memory cache. More...

static void *	__kmem_cache_alloc_slab (kmem_cache_t cachep, page_t slab_page)
	Allocates an object from a specified slab page. More...

static int	__kmem_cache_free_slab (kmem_cache_t cachep, page_t slab_page)
	Frees a slab page and updates the associated cache statistics. More...

int	kmem_cache_init (void)
	Initializes the kernel memory cache system. More...

kmem_cache_t *	kmem_cache_create (const char *name, unsigned int size, unsigned int align, slab_flags_t flags, kmem_fun_t ctor, kmem_fun_t dtor)
	Creates a new kmem_cache structure. More...

int	kmem_cache_destroy (kmem_cache_t *cachep)
	Destroys a specified kmem_cache structure. More...

void *	kmem_cache_alloc (kmem_cache_t *cachep, gfp_t flags)
	Allocates an object from the specified kmem_cache_t. More...

void	kmem_cache_free (void *ptr)
	Frees an object previously allocated from a kmem_cache_t. More...

void *	kmalloc (unsigned int size)
	Allocates memory of the specified size using kmalloc. More...

void	kfree (void *ptr)
	Frees memory allocated by kmalloc or kmem_cache_alloc. More...

Variables
static list_head	kmem_caches_list
	List of all active memory caches in the system.

static kmem_cache_t	kmem_cache
	Cache used for managing metadata about the memory caches themselves.

static kmem_cache_t *	malloc_blocks [MAX_KMALLOC_CACHE_ORDER]
	Array of slab caches for different orders of kmalloc.

Detailed Description

Memory slab allocator implementation in kernel. This file provides functions for managing memory allocation using the slab allocator technique. Slab allocators are efficient in managing frequent small memory allocations with minimal fragmentation.

Copyright: (c) 2014-2024 This file is distributed under the MIT License. See LICENSE.md for details.

Macro Definition Documentation

◆ ADDR_FROM_KMEM_OBJ

#define ADDR_FROM_KMEM_OBJ ( object ) ((void *)(object))

Macro to get the address from a kmem_obj structure.

Parameters

object Pointer to the kmem_obj structure.

Returns: Address of the object as a void *.

◆ KMEM_MAX_REFILL_OBJ_COUNT

#define KMEM_MAX_REFILL_OBJ_COUNT 64

Maximum number of objects to refill in a slab cache at once.

This defines the upper limit on how many objects to replenish in the slab when it runs out of free objects.

◆ KMEM_OBJ_FROM_ADDR

#define KMEM_OBJ_FROM_ADDR ( addr ) ((kmem_obj_t *)(addr))

Macro to convert an address into a kmem_obj pointer.

Parameters

addr	Address of the object.

Returns: Pointer to a kmem_obj structure.

◆ KMEM_OBJ_OVERHEAD

#define KMEM_OBJ_OVERHEAD sizeof(kmem_obj_t)

Overhead size for each memory object in the slab cache.

This defines the extra space required for managing the object, including the kmem_obj structure itself.

◆ KMEM_START_OBJ_COUNT

#define KMEM_START_OBJ_COUNT 8

Initial object count for each slab.

The starting number of objects in a newly allocated slab cache.

◆ MAX_KMALLOC_CACHE_ORDER

#define MAX_KMALLOC_CACHE_ORDER 12

Maximum order of kmalloc cache allocations.

If a requested memory allocation exceeds this order, a raw page allocation is done instead of using the slab cache.

Typedef Documentation

◆ kmem_obj_t

typedef struct kmem_obj kmem_obj_t

Structure to represent an individual memory object within a slab.

This structure is used to manage individual objects allocated from the slab. It contains a linked list to connect objects in the cache.

Function Documentation

◆ __alloc_slab_page()

static int __alloc_slab_page	(	kmem_cache_t *	cachep,
		gfp_t	flags
	)

static

Allocates and initializes a new slab page for a memory cache.

Parameters

cachep	Pointer to the memory cache (`kmem_cache_t`) for which a new slab page is being allocated.
flags	Allocation flags (e.g., GFP_KERNEL) passed to control memory allocation behavior.

Returns: 0 on success, -1 on failure.

◆ __compute_size_and_order()

static int __compute_size_and_order ( kmem_cache_t * cachep )

static

Computes and sets the size and gfp order for a memory cache.

This function adjusts the size of objects in the cache based on padding and alignment requirements, and calculates the gfp_order (number of contiguous pages) needed for slab allocations.

Parameters

cachep Pointer to the memory cache (kmem_cache_t) whose size and order are being computed.

Returns: 0 on success, -1 on failure.

◆ __kmem_cache_alloc_slab()

static void* __kmem_cache_alloc_slab	(	kmem_cache_t *	cachep,
		page_t *	slab_page
	)

inlinestatic

Allocates an object from a specified slab page.

This function retrieves a free object from the given slab page's free list. It decrements the count of free objects in both the slab page and the cache. If the constructor function is defined, it will be called to initialize the object.

Parameters

cachep	Pointer to the cache from which the object is being allocated.
slab_page	Pointer to the slab page from which to allocate the object.

Returns: Pointer to the allocated object, or NULL if allocation fails.

◆ __kmem_cache_create()

static int __kmem_cache_create	(	kmem_cache_t *	cachep,
		const char *	name,
		unsigned int	size,
		unsigned int	align,
		slab_flags_t	flags,
		kmem_fun_t	ctor,
		kmem_fun_t	dtor,
		unsigned int	start_count
	)

static

Initializes and creates a new memory cache.

This function sets up a new memory cache (kmem_cache_t) with the provided parameters such as object size, alignment, constructor/destructor functions, and flags. It also initializes slab lists, computes the appropriate size and order, refills the cache with objects, and adds it to the global cache list.

Parameters

cachep	Pointer to the memory cache structure to initialize.
name	Name of the cache.
size	Size of the objects to be allocated from the cache.
align	Alignment requirement for the objects.
flags	Slab allocation flags.
ctor	Constructor function to initialize objects (optional, can be NULL).
dtor	Destructor function to clean up objects (optional, can be NULL).
start_count	Initial number of objects to populate in the cache.

Returns: 0 on success, -1 on failure.

◆ __kmem_cache_free_slab()

static int __kmem_cache_free_slab	(	kmem_cache_t *	cachep,
		page_t *	slab_page
	)

inlinestatic

Frees a slab page and updates the associated cache statistics.

This function updates the total and free object counts in the cache and resets the slab page's metadata to indicate that it is no longer in use. It also frees the memory associated with the slab page.

Parameters

cachep	Pointer to the cache from which the slab page is being freed.
slab_page	Pointer to the slab page to be freed.

Returns: Returns 0 on success, or -1 if an error occurs.

◆ __kmem_cache_refill()

static int __kmem_cache_refill	(	kmem_cache_t *	cachep,
		unsigned int	free_num,
		gfp_t	flags
	)

static

Refills a memory cache with new slab pages to reach a specified number of free objects.

This function allocates new slab pages as needed until the cache has at least free_num free objects. If a page allocation fails, the refill process is aborted.

Parameters

cachep	Pointer to the memory cache (`kmem_cache_t`) that needs to be refilled.
free_num	The desired number of free objects in the cache.
flags	Allocation flags used for controlling memory allocation behavior (e.g., GFP_KERNEL).

Returns: 0 on success, -1 on failure.

◆ kfree()

void kfree ( void * ptr )

Frees memory allocated by kmalloc or kmem_cache_alloc.

Parameters

ptr	Pointer to the memory to free.

◆ kmalloc()

void* kmalloc ( unsigned int size )

Allocates memory of the specified size using kmalloc.

Parameters

size	Size of the memory to allocate.

Returns: Pointer to the allocated memory, or NULL if allocation fails.

◆ kmem_cache_alloc()

void* kmem_cache_alloc	(	kmem_cache_t *	cachep,
		gfp_t	flags
	)

Allocates an object from the specified kmem_cache_t.

Parameters

cachep	Pointer to the cache from which to allocate the object.
flags	Flags for the allocation (e.g., GFP_KERNEL).

Returns: Pointer to the allocated object, or NULL if allocation fails.

◆ kmem_cache_create()

kmem_cache_t* kmem_cache_create	(	const char *	name,
		unsigned int	size,
		unsigned int	align,
		slab_flags_t	flags,
		kmem_fun_t	ctor,
		kmem_fun_t	dtor
	)

Creates a new kmem_cache structure.

This function allocates memory for a new cache and initializes it with the provided parameters. The cache is ready for use after this function returns.

Parameters

name	Name of the cache.
size	Size of each object in the cache.
align	Alignment requirement for objects in the cache.
flags	Flags for slab allocation.
ctor	Constructor function for initializing objects (can be NULL).
dtor	Destructor function for cleaning up objects (can be NULL).

Returns: Pointer to the newly created kmem_cache_t, or NULL if allocation fails.

◆ kmem_cache_destroy()

int kmem_cache_destroy ( kmem_cache_t * cachep )

Destroys a specified kmem_cache structure.

This function cleans up and frees all memory associated with the specified cache, including all associated slab pages. After calling this function, the cache should no longer be used.

Parameters

cachep Pointer to the kmem_cache_t structure to destroy.

Returns: Returns 0 on success, or -1 if an error occurs.

◆ kmem_cache_free()

void kmem_cache_free ( void * addr )

Frees an object previously allocated from a kmem_cache_t.

Parameters

addr	Pointer to the object to free.

◆ kmem_cache_init()

int kmem_cache_init ( void )

Initializes the kernel memory cache system.

This function initializes the global cache list and creates the main cache for managing kmem_cache_t structures. It also creates caches for different order sizes for kmalloc allocations.

Note: This function should be called during system initialization.

Returns: Returns 0 on success, or -1 if an error occurs.

Classes

Macros

Typedefs

Functions

Variables

Detailed Description

Macro Definition Documentation

◆ ADDR_FROM_KMEM_OBJ

◆ KMEM_MAX_REFILL_OBJ_COUNT

◆ KMEM_OBJ_FROM_ADDR

◆ KMEM_OBJ_OVERHEAD

◆ KMEM_START_OBJ_COUNT

◆ MAX_KMALLOC_CACHE_ORDER

Typedef Documentation

◆ kmem_obj_t

Function Documentation

◆ __alloc_slab_page()

◆ __compute_size_and_order()

◆ __kmem_cache_alloc_slab()

◆ __kmem_cache_create()

◆ __kmem_cache_free_slab()

◆ __kmem_cache_refill()

◆ kfree()

◆ kmalloc()

◆ kmem_cache_alloc()

◆ kmem_cache_create()

◆ kmem_cache_destroy()

◆ kmem_cache_free()

◆ kmem_cache_init()