C Specification
Bits which may be set in VkMemoryType::propertyFlags
,
indicating properties of a memory type, are:
// Provided by VK_VERSION_1_0
typedef enum VkMemoryPropertyFlagBits {
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT = 0x00000001,
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT = 0x00000002,
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT = 0x00000004,
VK_MEMORY_PROPERTY_HOST_CACHED_BIT = 0x00000008,
VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT = 0x00000010,
// Provided by VK_VERSION_1_1
VK_MEMORY_PROPERTY_PROTECTED_BIT = 0x00000020,
// Provided by VK_AMD_device_coherent_memory
VK_MEMORY_PROPERTY_DEVICE_COHERENT_BIT_AMD = 0x00000040,
// Provided by VK_AMD_device_coherent_memory
VK_MEMORY_PROPERTY_DEVICE_UNCACHED_BIT_AMD = 0x00000080,
// Provided by VK_NV_external_memory_rdma
VK_MEMORY_PROPERTY_RDMA_CAPABLE_BIT_NV = 0x00000100,
} VkMemoryPropertyFlagBits;
Description
-
VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT
bit specifies that memory allocated with this type is the most efficient for device access. This property will be set if and only if the memory type belongs to a heap with theVK_MEMORY_HEAP_DEVICE_LOCAL_BIT
set. -
VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT
bit specifies that memory allocated with this type can be mapped for host access using vkMapMemory. -
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT
bit specifies that the host cache management commands vkFlushMappedMemoryRanges and vkInvalidateMappedMemoryRanges are not needed to flush host writes to the device or make device writes visible to the host, respectively. -
VK_MEMORY_PROPERTY_HOST_CACHED_BIT
bit specifies that memory allocated with this type is cached on the host. Host memory accesses to uncached memory are slower than to cached memory, however uncached memory is always host coherent. -
VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT
bit specifies that the memory type only allows device access to the memory. Memory types must not have bothVK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT
andVK_MEMORY_PROPERTY_HOST_VISIBLE_BIT
set. Additionally, the object’s backing memory may be provided by the implementation lazily as specified in Lazily Allocated Memory. -
VK_MEMORY_PROPERTY_PROTECTED_BIT
bit specifies that the memory type only allows device access to the memory, and allows protected queue operations to access the memory. Memory types must not haveVK_MEMORY_PROPERTY_PROTECTED_BIT
set and any ofVK_MEMORY_PROPERTY_HOST_VISIBLE_BIT
set, orVK_MEMORY_PROPERTY_HOST_COHERENT_BIT
set, orVK_MEMORY_PROPERTY_HOST_CACHED_BIT
set. -
VK_MEMORY_PROPERTY_DEVICE_COHERENT_BIT_AMD
bit specifies that device accesses to allocations of this memory type are automatically made available and visible. -
VK_MEMORY_PROPERTY_DEVICE_UNCACHED_BIT_AMD
bit specifies that memory allocated with this type is not cached on the device. Uncached device memory is always device coherent. -
VK_MEMORY_PROPERTY_RDMA_CAPABLE_BIT_NV
bit specifies that external devices can access this memory directly.
For any memory allocated with both the
VK_MEMORY_PROPERTY_HOST_COHERENT_BIT
and the
VK_MEMORY_PROPERTY_DEVICE_COHERENT_BIT_AMD
, host or device accesses
also perform automatic memory domain transfer operations, such that writes
are always automatically available and visible to both host and device
memory domains.
Note
Device coherence is a useful property for certain debugging use cases (e.g. crash analysis, where performing separate coherence actions could mean values are not reported correctly). However, device coherent accesses may be slower than equivalent accesses without device coherence, particularly if they are also device uncached. For device uncached memory in particular, repeated accesses to the same or neighbouring memory locations over a short time period (e.g. within a frame) may be slower than it would be for the equivalent cached memory type. As such, it is generally inadvisable to use device coherent or device uncached memory except when really needed. |
Document Notes
For more information, see the Vulkan Specification
This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.