OS Virtual Memory

Low-level OS page reservation, commitment, decommitment, and release. More...

Functions
void *	os_mem_reserve (usize size)
	Reserves a block of virtual address space.
b32	os_mem_commit (void *ptr, usize size)
	Commits physical RAM to a previously reserved address range.
void	os_mem_decommit (void *ptr, usize size)
	Decommits physical RAM, returning it to the OS while keeping the address space.
void	os_mem_release (void *ptr, usize size)
	Releases a reserved virtual address range entirely back to the OS.

Detailed Description

Low-level OS page reservation, commitment, decommitment, and release.

Function Documentation

os_mem_commit()

b32 os_mem_commit	(	void *	ptr,
		usize	size )

Commits physical RAM to a previously reserved address range.

Note

The committed memory is zero-initialized by the OS on first access.

Parameters

ptr	Pointer within a previously reserved block.
size	Number of bytes to commit (rounded up to the OS page size internally).

Returns

1 (true) on success, 0 (false) if the OS refused (e.g., out of physical RAM).

Definition at line 29 of file mem_os.c.

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os_mem_decommit()

void os_mem_decommit	(	void *	ptr,
		usize	size )

Decommits physical RAM, returning it to the OS while keeping the address space.

Note

The virtual address range remains reserved and valid for a future os_mem_commit(). Any attempt to read or write decommitted memory before recommitting it is undefined behavior (access violation / segfault).

Parameters

ptr	Pointer to the start of the committed range.
size	Number of bytes to decommit.

Definition at line 39 of file mem_os.c.

os_mem_release()

void os_mem_release	(	void *	ptr,
		usize	size )

Releases a reserved virtual address range entirely back to the OS.

Warning

After this call, ptr is invalid. Any access is undefined behavior.

Note

On Windows, size is ignored (the OS tracks the full reservation size). On POSIX, size must match the value passed to os_mem_reserve().

Parameters

ptr	Pointer returned by os_mem_reserve().
size	Total size that was originally passed to os_mem_reserve().

Definition at line 50 of file mem_os.c.

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os_mem_reserve()

void * os_mem_reserve

(

usize

size

)

Reserves a block of virtual address space.

Note

Uses ZERO physical RAM. The returned pointer cannot be read or written until the range (or a sub-range) is committed with os_mem_commit().

Parameters

size	The number of bytes to reserve. Can safely be in the gigabyte range.

Returns

Pointer to the start of the reserved range, or NULL on failure.

Definition at line 18 of file mem_os.c.

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