MEMORY_REGION_INFORMATION - NtDoc

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

// private
typedef struct _MEMORY_REGION_INFORMATION
{
    PVOID AllocationBase;
    ULONG AllocationProtect;
    union
    {
        ULONG RegionType;
        struct
        {
            ULONG Private : 1;
            ULONG MappedDataFile : 1;
            ULONG MappedImage : 1;
            ULONG MappedPageFile : 1;
            ULONG MappedPhysical : 1;
            ULONG DirectMapped : 1;
            ULONG SoftwareEnclave : 1; // REDSTONE3
            ULONG PageSize64K : 1;
            ULONG PlaceholderReservation : 1; // REDSTONE4
            ULONG MappedAwe : 1; // 21H1
            ULONG MappedWriteWatch : 1;
            ULONG PageSizeLarge : 1;
            ULONG PageSizeHuge : 1;
            ULONG Reserved : 19;
        };
    };
    SIZE_T RegionSize;
    SIZE_T CommitSize;
    ULONG_PTR PartitionId; // 19H1
    ULONG_PTR NodePreference; // 20H1
} MEMORY_REGION_INFORMATION, *PMEMORY_REGION_INFORMATION;

#endif

View code on GitHub

This structure is documented in Windows SDK.