## C Specification

If the pNext chain of VkMemoryAllocateInfo includes a VkMemoryAllocateFlagsInfo structure, then that structure includes flags and a device mask controlling how many instances of the memory will be allocated.

The VkMemoryAllocateFlagsInfo structure is defined as:

typedef struct VkMemoryAllocateFlagsInfo {
VkStructureType          sType;
const void*              pNext;
VkMemoryAllocateFlags    flags;
} VkMemoryAllocateFlagsInfo;

or the equivalent

typedef VkMemoryAllocateFlagsInfo VkMemoryAllocateFlagsInfoKHR;

## Members

• sType is the type of this structure.

• pNext is NULL or a pointer to an extension-specific structure.

• flags is a bitmask of VkMemoryAllocateFlagBits controlling the allocation.

• deviceMask is a mask of physical devices in the logical device, indicating that memory must be allocated on each device in the mask, if VK_MEMORY_ALLOCATE_DEVICE_MASK_BIT is set in flags.

## Description

If VK_MEMORY_ALLOCATE_DEVICE_MASK_BIT is not set, the number of instances allocated depends on whether VK_MEMORY_HEAP_MULTI_INSTANCE_BIT is set in the memory heap. If VK_MEMORY_HEAP_MULTI_INSTANCE_BIT is set, then memory is allocated for every physical device in the logical device (as if deviceMask has bits set for all device indices). If VK_MEMORY_HEAP_MULTI_INSTANCE_BIT is not set, then a single instance of memory is allocated (as if deviceMask is set to one).

On some implementations, allocations from a multi-instance heap may consume memory on all physical devices even if the deviceMask excludes some devices. If VkPhysicalDeviceGroupProperties::subsetAllocation is VK_TRUE, then memory is only consumed for the devices in the device mask.

 Note In practice, most allocations on a multi-instance heap will be allocated across all physical devices. Unicast allocation support is an optional optimization for a minority of allocations.
Valid Usage
• If VK_MEMORY_ALLOCATE_DEVICE_MASK_BIT is set, deviceMask must be a valid device mask.

• If VK_MEMORY_ALLOCATE_DEVICE_MASK_BIT is set, deviceMask must not be zero

Valid Usage (Implicit)
• sType must be VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_FLAGS_INFO

• flags must be a valid combination of VkMemoryAllocateFlagBits values