NtFreeVirtualMemory - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers 
#ifndef _NTMMAPI_H
// Virtual memory
#if (PHNT_MODE != PHNT_MODE_KERNEL)

NTSYSCALLAPI
NTSTATUS
NTAPI
NtFreeVirtualMemory(
    _In_ HANDLE ProcessHandle,
    _Inout_ PVOID *BaseAddress,
    _Inout_ PSIZE_T RegionSize,
    _In_ ULONG FreeType
    );

#endif
#endif

View code on GitHub
#ifndef _NTZWAPI_H

NTSYSCALLAPI
NTSTATUS
NTAPI
ZwFreeVirtualMemory(
    _In_ HANDLE ProcessHandle,
    _Inout_ PVOID *BaseAddress,
    _Inout_ PSIZE_T RegionSize,
    _In_ ULONG FreeType
    );

#endif

View code on GitHub

This function is documented in Windows Driver Kit here and here.

RegionSize

If you put pointer to NULL value as RegionSize, system will free all region, and put size of it in result.

FreeType

Can be one of the values: MEM_DECOMMIT, or MEM_RELEASE.

Documented by

See also

Edit description on GitHub