Kernel Heap (kmalloc/kfree)

Boundary-tag kernel heap allocator at HEAP_START (0xFFFF820000000000). More...

Functions
void	heap_init (void)
	Maps the first heap page at HEAP_START via vmm_map_page() and writes the initial free-block boundary tag covering the entire heap region. Must be called exactly once during boot before any call to kmalloc(). Called by kernel_main() after vmm setup.
void *	kmalloc (size_t size)
	Uses a first-fit boundary-tag strategy. Acquires heap_lock (spinlock_irqsave) before scanning. Maps additional pages via vmm_map_page() if the current heap extent is exhausted (up to HEAP_MAX).
void	kfree (void *ptr)
	Marks the block free in its boundary tag and coalesces adjacent free blocks (forward and backward). Acquires heap_lock before modifying heap state.
size_t	heap_free_bytes (void)
	Walks the boundary-tag chain and sums the sizes of all free blocks. O(n) in the number of heap blocks. Intended for diagnostic/debug output only.

Detailed Description

Boundary-tag kernel heap allocator at HEAP_START (0xFFFF820000000000).

Implements a simple first-fit boundary-tag heap that grows upward from HEAP_START. Maximum size is HEAP_MAX - HEAP_START = 4 MiB. Not thread-safe on its own; callers must hold heap_lock (a spinlock in heap.c) in SMP context.

Function Documentation

heap_free_bytes()

size_t heap_free_bytes

(

void

)

Walks the boundary-tag chain and sums the sizes of all free blocks. O(n) in the number of heap blocks. Intended for diagnostic/debug output only.

heap_free_bytes() - Query the total free bytes currently available in the heap.

Returns

Total free bytes across all free blocks in the heap.

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heap_init()

void heap_init

(

void

)

Maps the first heap page at HEAP_START via vmm_map_page() and writes the initial free-block boundary tag covering the entire heap region. Must be called exactly once during boot before any call to kmalloc(). Called by kernel_main() after vmm setup.

heap_init() - Initialise the kernel heap allocator.

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kfree()

void kfree

(

void *

ptr

)

Marks the block free in its boundary tag and coalesces adjacent free blocks (forward and backward). Acquires heap_lock before modifying heap state.

kfree() - Return a kmalloc'd allocation to the kernel heap free list.

Parameters

ptr	Pointer returned by a previous kmalloc() call. Passing NULL is a no-op.

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kmalloc()

void * kmalloc

(

size_t

size

)

Uses a first-fit boundary-tag strategy. Acquires heap_lock (spinlock_irqsave) before scanning. Maps additional pages via vmm_map_page() if the current heap extent is exhausted (up to HEAP_MAX).

kmalloc() - Allocate @size bytes from the kernel heap.

Parameters

size	Number of bytes to allocate. Rounded up to 8-byte alignment internally.

Returns

8-byte-aligned pointer to allocated memory, or NULL on OOM.

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