FREE_VIRTUAL_MEMORY_EX_CALLBACK - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTRTL_H

typedef NTSTATUS FREE_VIRTUAL_MEMORY_EX_CALLBACK(
    _Inout_ HANDLE CallbackContext,
    _In_ HANDLE ProcessHandle,
    _Inout_ __drv_freesMem(Mem) PVOID *BaseAddress,
    _Inout_ PSIZE_T RegionSize,
    _In_ ULONG FreeType
    );

#endif

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This callback function is documented in Windows Driver Kit.