// Copyright (c) 2015-2016 The Khronos Group Inc. // Copyright notice at https://www.khronos.org/registry/speccopyright.html [[memory]] = Memory Allocation {apiname} memory is broken up into two categories, _host memory_ and _device memory_. [[memory-host]] == Host Memory Host memory is memory needed by the {apiname} implementation for non-device-visible storage. This storage may: be used for e.g. internal software structures. [[memory-allocation]] {apiname} provides applications the opportunity to perform host memory allocations on behalf of the {apiname} implementation. If this feature is not used, the implementation will perform its own memory allocations. Since most memory allocations are off the critical path, this is not meant as a performance feature. Rather, this can: be useful for certain embedded systems, for debugging purposes (e.g. putting a guard page after all host allocations), or for memory allocation logging. Allocators are provided by the application as a pointer to a sname:VkAllocationCallbacks structure: include::../structs/VkAllocationCallbacks.txt[] * pname:pUserData is a value to be interpreted by the implementation of the callbacks. When any of the callbacks in sname:VkAllocationCallbacks are called, the {apiname} implementation will pass this value as the first parameter to the callback. This value can: vary each time an allocator is passed into a command, even when the same object takes an allocator in multiple commands. * pname:pfnAllocation is a pointer to an application-defined memory allocation function of type tlink:PFN_vkAllocationFunction. * pname:pfnReallocation is a pointer to an application-defined memory reallocation function of type tlink:PFN_vkReallocationFunction. * pname:pfnFree is a pointer to an application-defined memory free function of type tlink:PFN_vkFreeFunction. * pname:pfnInternalAllocation is a pointer to an application-defined function that is called by the implementation when the implementation makes internal allocations, and it is of type tlink:PFN_vkInternalAllocationNotification. * pname:pfnInternalFree is a pointer to an application-defined function that is called by the implementation when the implementation frees internal allocations, and it is of type tlink:PFN_vkInternalFreeNotification. include::../validity/structs/VkAllocationCallbacks.txt[] The type of pname:pfnAllocation is: include::../funcpointers/PFN_vkAllocationFunction.txt[] * pname:pUserData is the value specified for slink:VkAllocationCallbacks.pUserData in the allocator specified by the application. * pname:size is the size in bytes of the requested allocation. * pname:alignment is the requested alignment of the allocation in bytes and must: be a power of two. * pname:allocationScope is a elink:VkSystemAllocationScope value specifying the scope of the lifetime of the allocation, as described <>. [[vkAllocationFunction_return_rules]] If pname:pfnAllocation is unable to allocate the requested memory, it must: return `NULL`. If the allocation was successful, it must: return a valid pointer to memory allocation containing at least pname:size bytes, and with the pointer value being a multiple of pname:alignment. [NOTE] ==== Correct Vulkan operation cannot: be assumed if the application doesn't follow these rules. For example, pname:pfnAllocation (or pname:pfnReallocation) could cause termination of running Vulkan instance(s) on a failed allocation for debugging purposes, either directly or indirectly. In these circumstances, it cannot: be assumed that any part of any affected VkInstance objects are going to operate correctly (even flink:vkDestroyInstance), and the application must: ensure it cleans up properly via other means (e.g. process termination). ==== If pname:pfnAllocation returns `NULL`, and if the implementation is unable to continue correct processing of the current command without the requested allocation, it must: treat this as a run-time error, and generate ename:VK_ERROR_OUT_OF_HOST_MEMORY at the appropriate time for the command in which the condition was detected, as described in <>. If the implementation is able to continue correct processing of the current command without the requested allocation, then it may: do so, and must: not generate ename:VK_ERROR_OUT_OF_HOST_MEMORY as a result of this failed allocation. The type of pname:pfnReallocation is: include::../funcpointers/PFN_vkReallocationFunction.txt[] * pname:pUserData is the value specified for slink:VkAllocationCallbacks.pUserData in the allocator specified by the application. * pname:pOriginal must: be either `NULL` or a pointer previously returned by pname:pfnReallocation or pname:pfnAllocation of the same allocator. * pname:size is the size in bytes of the requested allocation. * pname:alignment is the requested alignment of the allocation in bytes and must: be a power of two. * pname:allocationScope is a elink:VkSystemAllocationScope value specifying the scope of the lifetime of the allocation, as described <>. pname:pfnReallocation must: return an allocation with enough space for pname:size bytes, and the contents of the original allocation from bytes zero to latexmath:[$\min(\textrm{original size, new size})-1$] must: be preserved in the returned allocation. If pname:size is larger than the old size, the contents of the additional space are undefined. If satisfying these requirements involves creating a new allocation, then the old allocation should: be freed. If pname:pOriginal is `NULL`, then pname:pfnReallocation must: behave equivalently to a call to tlink:PFN_vkAllocationFunction with the same parameter values (without pname:pOriginal). If pname:size is zero, then pname:pfnReallocation must: behave equivalently to a call to tlink:PFN_vkFreeFunction with the same pname:pUserData parameter value, and pname:pMemory equal to pname:pOriginal. If pname:pOriginal is non-`NULL`, the implementation must: ensure that pname:alignment is equal to the pname:alignment used to originally allocate pname:pOriginal. If this function fails and pname:pOriginal is non-`NULL` the application must: not free the old allocation. pname:pfnReallocation must: follow the same <>. The type of pname:pfnFree is: include::../funcpointers/PFN_vkFreeFunction.txt[] * pname:pUserData is the value specified for slink:VkAllocationCallbacks.pUserData in the allocator specified by the application. * pname:pMemory is the allocation to be freed. pname:pMemory may: be `NULL`, which the callback must: handle safely. If pname:pMemory is non-`NULL`, it must: be a pointer previously allocated by pname:pfnAllocation or pname:pfnReallocation. The application should: free this memory. The type of pname:pfnInternalAllocation is: include::../funcpointers/PFN_vkInternalAllocationNotification.txt[] * pname:pUserData is the value specified for slink:VkAllocationCallbacks.pUserData in the allocator specified by the application. * pname:size is the requested size of an allocation. * pname:allocationType is the requested type of an allocation. * pname:allocationScope is a elink:VkSystemAllocationScope value specifying the scope of the lifetime of the allocation, as described <>. This is a purely informational callback. The type of pname:pfnInternalFree is: include::../funcpointers/PFN_vkInternalFreeNotification.txt[] * pname:pUserData is the value specified for slink:VkAllocationCallbacks.pUserData in the allocator specified by the application. * pname:size is the requested size of an allocation. * pname:allocationType is the requested type of an allocation. * pname:allocationScope is a elink:VkSystemAllocationScope value specifying the scope of the lifetime of the allocation, as described <>. [[memory-host-allocation-scope]] Each allocation has a _scope_ which defines its lifetime and which object it is associated with. The scope is provided in the pname:allocationScope parameter and takes a value of type elink:VkSystemAllocationScope: include::../enums/VkSystemAllocationScope.txt[] * ename:VK_SYSTEM_ALLOCATION_SCOPE_COMMAND - The allocation is scoped to the duration of the {apiname} command. * ename:VK_SYSTEM_ALLOCATION_SCOPE_OBJECT - The allocation is scoped to the lifetime of the {apiname} object that is being created or used. * ename:VK_SYSTEM_ALLOCATION_SCOPE_CACHE - The allocation is scoped to the lifetime of a sname:VkPipelineCache object. * ename:VK_SYSTEM_ALLOCATION_SCOPE_DEVICE - The allocation is scoped to the lifetime of the {apiname} device. * ename:VK_SYSTEM_ALLOCATION_SCOPE_INSTANCE - The allocation is scoped to the lifetime of the {apiname} instance. Most {apiname} commands operate on a single object, or there is a sole object that is being created or manipulated. When an allocation uses a scope of ename:VK_SYSTEM_ALLOCATION_SCOPE_OBJECT or ename:VK_SYSTEM_ALLOCATION_SCOPE_CACHE, the allocation is scoped to the object being created or manipulated. When an implementation requires host memory, it will make callbacks to the application using the most specific allocator and scope available: * If an allocation is scoped to the duration of a command, the allocator will use the ename:VK_SYSTEM_ALLOCATION_SCOPE_COMMAND scope. The most specific allocator available is used: if the object being created or manipulated has an allocator, that object's allocator will be used, else if the parent sname:VkDevice has an allocator it will be used, else if the parent sname:VkInstance has an allocator it will be used. Else, * If an allocation is associated with an object of type sname:VkPipelineCache, the allocator will use the ename:VK_SYSTEM_ALLOCATION_SCOPE_CACHE scope. The most specific allocator available is used (pipeline cache, else device, else instance). Else, * If an allocation is scoped to the lifetime of an object, that object is being created or manipulated by the command, and that object's type is not sname:VkDevice or sname:VkInstance, the allocator will use a scope of ename:VK_SYSTEM_ALLOCATION_SCOPE_OBJECT. The most specific allocator available is used (object, else device, else instance). Else, * If an allocation is scoped to the lifetime of a device, the allocator will use scope of ename:VK_SYSTEM_ALLOCATION_SCOPE_DEVICE. The most specific allocator available is used (device, else instance). Else, * If the allocation is scoped to the lifetime of an instance and the instance has an allocator, its allocator will be used with a scope of ename:VK_SYSTEM_ALLOCATION_SCOPE_INSTANCE. * Otherwise an implementation will allocate memory through an alternative mechanism that is unspecified. Objects that are allocated from pools do not specify their own allocator. When an implementation requires host memory for such an object, that memory is sourced from the object's parent pool's allocator. The application is not expected to handle allocating memory that is intended for execution by the host due to the complexities of differing security implementations across multiple platforms. The implementation will allocate such memory internally and invoke an application provided informational callback when these _internal allocations_ are allocated and freed. Upon allocation of executable memory, pname:pfnInternalAllocation will be called. Upon freeing executable memory, pname:pfnInternalFree will be called. An implementation will only call an informational callback for executable memory allocations and frees. The pname:allocationType parameter to the pname:pfnInternalAllocation and pname:pfnInternalFree functions may: be one of the following values: include::../enums/VkInternalAllocationType.txt[] * ename:VK_INTERNAL_ALLOCATION_TYPE_EXECUTABLE - The allocation is intended for execution by the host. An implementation must: only make calls into an application-provided allocator from within the scope of an API command. An implementation must: only make calls into an application-provided allocator from the same thread that called the provoking API command. The implementation shouldnot: synchronize calls to any of the callbacks. If synchronization is needed, the callbacks must: provide it themselves. The informational callbacks are subject to the same restrictions as the allocation callbacks. If an implementation intends to make calls through an sname:VkAllocationCallbacks structure between the time a ftext:vkCreate* command returns and the time a corresponding ftext:vkDestroy* command begins, that implementation must: save a copy of the allocator before the ftext:vkCreate* command returns. The callback functions and any data structures they rely upon must: remain valid for the lifetime of the object they are associated with. If an allocator is provided to a ftext:vkCreate* command, a _compatible_ allocator must: be provided to the corresponding ftext:vkDestroy* command. Two sname:VkAllocationCallbacks structures are compatible if memory created with pname:pfnAllocation or pname:pfnReallocation in each can: be freed with pname:pfnReallocation or pname:pfnFree in the other. An allocator must: not be provided to a ftext:vkDestroy* command if an allocator was not provided to the corresponding ftext:vkCreate* command. If a non-`NULL` allocator is used, the pname:pfnAllocation, pname:pfnReallocation and pname:pfnFree members must: be non-`NULL` and point to valid implementations of the callbacks. An application can: choose to not provide informational callbacks by setting both pname:pfnInternalAllocation and pname:pfnInternalFree to `NULL`. pname:pfnInternalAllocation and pname:pfnInternalFree must: either both be `NULL` or both be non-`NULL`. If pname:pfnAllocation or pname:pfnReallocation fail, the implementation may: fail object creation and/or generate an ename:VK_ERROR_OUT_OF_HOST_MEMORY error, as appropriate. Allocation callbacks must: not call any {apiname} commands. The following sets of rules define when an implementation is permitted to call the allocator callbacks. pname:pfnAllocation or pname:pfnReallocation may: be called in the following situations: * Host memory scoped to the lifetime of a sname:VkDevice or sname:VkInstance may: be allocated from any API command. * Host memory scoped to the duration of a command may: be allocated from any API command. * Host memory scoped to the lifetime of a sname:VkPipelineCache may: only be allocated from: ** fname:vkCreatePipelineCache ** fname:vkMergePipelineCaches for pname:dstCache ** fname:vkCreateGraphicsPipelines for pname:pPipelineCache ** fname:vkCreateComputePipelines for pname:pPipelineCache * Host memory scoped to the lifetime of a sname:VkDescriptorPool may: only be allocated from: ** any command that takes the pool as a direct argument ** fname:vkAllocateDescriptorSets for the pname:descriptorPool member of its pname:pAllocateInfo parameter ** fname:vkCreateDescriptorPool * Host memory scoped to the lifetime of a sname:VkCommandPool may: only be allocated from: ** any command that takes the pool as a direct argument ** fname:vkCreateCommandPool ** fname:vkAllocateCommandBuffers for the pname:commandPool member of its pname:pAllocateInfo parameter ** any ftext:vkCmd* command whose pname:commandBuffer was created from that sname:VkCommandPool * Host memory scoped to the lifetime of any other object may: only be allocated in that object's ftext:vkCreate* command. pname:pfnFree may: be called in the following situations: * Host memory scoped to the lifetime of a sname:VkDevice or sname:VkInstance may: be freed from any API command. * Host memory scoped to the duration of a command must: be freed by any API command which allocates such memory. * Host memory scoped to the lifetime of a sname:VkPipelineCache may: be freed from fname:vkDestroyPipelineCache. * Host memory scoped to the lifetime of a sname:VkDescriptorPool may: be freed from ** any command that takes the pool as a direct argument * Host memory scoped to the lifetime of a sname:VkCommandPool may: be freed from: ** any command that takes the pool as a direct argument ** fname:vkResetCommandBuffer whose pname:commandBuffer was created from that sname:VkCommandPool * Host memory scoped to the lifetime of any other object may: be freed in that object's ftext:vkDestroy* command. * Any command that allocates host memory may: also free host memory of the same scope. [[memory-device]] == Device Memory Device memory is memory that is visible to the device, for example the contents of opaque images that can: be natively used by the device, or uniform buffer objects that reside in on-device memory. The memory properties of the physical device describe the memory heaps and memory types available to a physical device. These can: be queried by calling: include::../protos/vkGetPhysicalDeviceMemoryProperties.txt[] * pname:physicalDevice is the handle to the device to query. * pname:pMemoryProperties points to an instance of sname:VkPhysicalDeviceMemoryProperties structure in which the properties are returned. include::../validity/protos/vkGetPhysicalDeviceMemoryProperties.txt[] The sname:VkPhysicalDeviceMemoryProperties structure is defined as: include::../structs/VkPhysicalDeviceMemoryProperties.txt[] ifdef::editing-notes[] [NOTE] .editing-note ==== TODO (Jon) - Need to restructure description like other structures. ==== endif::editing-notes[] include::../validity/structs/VkPhysicalDeviceMemoryProperties.txt[] The sname:VkPhysicalDeviceMemoryProperties structure describes a number of _memory heaps_ as well as a number of _memory types_ that can: be used to access memory allocated in those heaps. Each heap describes a memory resource of a particular size, and each memory type describes a set of memory properties (e.g. host cached vs uncached) that can: be used with a given memory heap. Allocations using a particular memory type will consume resources from the heap indicated by that memory type's heap index. More than one memory type may: share each heap, and the heaps and memory types provide a mechanism to advertise an accurate size of the physical memory resources while allowing the memory to be used with a variety of different properties. The number of memory heaps is given by pname:memoryHeapCount and is less than or equal to ename:VK_MAX_MEMORY_HEAPS. Each heap is described by an element of the pname:memoryHeaps array, as a sname:VkMemoryHeap structure. The number of memory types available across all memory heaps is given by pname:memoryTypeCount and is less than or equal to ename:VK_MAX_MEMORY_TYPES. Each memory type is described by an element of the pname:memoryTypes array, as a sname:VkMemoryType structure. The sname:VkMemoryHeap structure is defined as: include::../structs/VkMemoryHeap.txt[] * pname:size is the total memory size in bytes in the heap. * pname:flags is a bitmask of attribute flags for the heap. The bits specified in pname:flags are: + include::../enums/VkMemoryHeapFlagBits.txt[] ** if pname:flags contains ename:VK_MEMORY_HEAP_DEVICE_LOCAL_BIT, it means the heap corresponds to device local memory. Device local memory may: have different performance characteristics than host local memory, and may: support different memory property flags. include::../validity/structs/VkMemoryHeap.txt[] At least one heap must: include ename:VK_MEMORY_HEAP_DEVICE_LOCAL_BIT in pname:flags. If there are multiple heaps that all have similar performance characteristics, they may: all include ename:VK_MEMORY_HEAP_DEVICE_LOCAL_BIT. In a unified memory architecture (UMA) system, there is often only a single memory heap which is considered to be equally ``local'' to the host and to the device, and such an implementation must: advertise the heap as device-local. The sname:VkMemoryType structure is defined as: include::../structs/VkMemoryType.txt[] * pname:heapIndex describes which memory heap this memory type corresponds to, and must: be less than pname:memoryHeapCount from the sname:VkPhysicalDeviceMemoryProperties structure. * pname:propertyFlags is a bitmask of properties for this memory type. The bits specified in pname:propertyFlags are: + include::../enums/VkMemoryPropertyFlagBits.txt[] ** if pname:propertyFlags has the ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT bit set, memory allocated with this type is the most efficient for device access. This property will only be set for memory types belonging to heaps with the ename:VK_MEMORY_HEAP_DEVICE_LOCAL_BIT set. ** if pname:propertyFlags has the ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT bit set, memory allocated with this type can: be mapped using flink:vkMapMemory so that it can: be accessed on the host. ** if pname:propertyFlags has the ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT bit set, host cache management commands fname:vkFlushMappedMemoryRanges and fname:vkInvalidateMappedMemoryRanges are not needed to make host writes visible to the device or device writes visible to the host, respectively. ** if pname:propertyFlags has the ename:VK_MEMORY_PROPERTY_HOST_CACHED_BIT bit set, 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. ** if pname:propertyFlags has the ename:VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT bit set, the memory type only allows device access to the memory. Memory types must: not have both ename:VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT and ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set. Additionally, the object's backing memory may: be provided by the implementation lazily as specified in <>. include::../validity/structs/VkMemoryType.txt[] Each memory type returned by flink:vkGetPhysicalDeviceMemoryProperties must: have its pname:propertyFlags set to one of the following values: * 0 * ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT * ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | ename:VK_MEMORY_PROPERTY_HOST_CACHED_BIT * ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | ename:VK_MEMORY_PROPERTY_HOST_CACHED_BIT | ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT * ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT * ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT | ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT * ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT | ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | ename:VK_MEMORY_PROPERTY_HOST_CACHED_BIT * ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT | ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT | ename:VK_MEMORY_PROPERTY_HOST_CACHED_BIT | ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT * ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT | ename:VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT There must: be at least one memory type with both the ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT and ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT bits set in its pname:propertyFlags. There must: be at least one memory type with the ename:VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT bit set in its pname:propertyFlags. The memory types are sorted according to a preorder which serves to aid in easily selecting an appropriate memory type. Given two memory types X and Y, the preorder defines latexmath:[$X \leq Y$] if: * the memory property bits set for X are a subset of the memory property bits set for Y. Or, * the memory property bits set for X are the same as the memory property bits set for Y, and X uses a memory heap with greater or equal performance (as determined in an implementation-specific manner). Memory types are ordered in the list such that X is assigned a lesser pname:memoryTypeIndex than Y if latexmath:[$X \leq Y \land \neg(Y \leq X)$] according to the preorder. Note that the list of all allowed memory property flag combinations above satisfies this preorder, but other orders would as well. The goal of this ordering is to enable applications to use a simple search loop in selecting the proper memory type, along the lines of: [source,{basebackend@docbook:c++:cpp}] --------------------------------------------------- // Find a memory type in "memoryTypeBits" that includes all of "properties" int32_t FindProperties(uint32_t memoryTypeBits, VkMemoryPropertyFlags properties) { for (int32_t i = 0; i < memoryTypeCount; ++i) { if ((memoryTypeBits & (1 << i)) && ((memoryTypes[i].propertyFlags & properties) == properties)) return i; } return -1; } // Try to find an optimal memory type, or if it does not exist // find any compatible memory type VkMemoryRequirements memoryRequirements; vkGetImageMemoryRequirements(device, image, &memoryRequirements); int32_t memoryType = FindProperties(memoryRequirements.memoryTypeBits, optimalProperties); if (memoryType == -1) memoryType = FindProperties(memoryRequirements.memoryTypeBits, requiredProperties); --------------------------------------------------- The loop will find the first supported memory type that has all bits requested in code:properties set. If there is no exact match, it will find a closest match (i.e. a memory type with the fewest additional bits set), which has some additional bits set but which are not detrimental to the behaviors requested by code:properties. The application can: first search for the optimal properties, e.g. a memory type that is device-local or supports coherent cached accesses, as appropriate for the intended usage, and if such a memory type is not present can: fallback to searching for a less optimal but guaranteed set of properties such as "0" or "host-visible and coherent". A {apiname} device operates on data in device memory via memory objects that are represented in the API by a sname:VkDeviceMemory handle. Memory objects are allocated by calling fname:vkAllocateMemory: include::../protos/vkAllocateMemory.txt[] * pname:device is the logical device that owns the memory. * pname:pAllocateInfo is a pointer to an instance of the slink:VkMemoryAllocateInfo structure describing parameters of the allocation. A successful returned allocation must: use the requested parameters -- no substitution is permitted by the implementation. * pname:pAllocator controls host memory allocation as described in the <> chapter. * pname:pMemory is a pointer to a sname:VkDeviceMemory handle in which information about the allocated memory is returned. include::../validity/protos/vkAllocateMemory.txt[] The sname:VkMemoryAllocateInfo structure is defined as: include::../structs/VkMemoryAllocateInfo.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:allocationSize is the size of the allocation in bytes * pname:memoryTypeIndex is the memory type index, which selects the properties of the memory to be allocated, as well as the heap the memory will come from. include::../validity/structs/VkMemoryAllocateInfo.txt[] Allocations returned by fname:vkAllocateMemory are guaranteed to meet any alignment requirement by the implementation. For example, if an implementation requires 128 byte alignment for images and 64 byte alignment for buffers, the device memory returned through this mechanism would be 128-byte aligned. This ensures that applications can: correctly suballocate objects of different types (with potentially different alignment requirements) in the same memory object. When memory is allocated, its contents are undefined. There is an implementation-dependent maximum number of memory allocations which can: be simultaneously created on a device. This is specified by the <> member of the sname:VkPhysicalDeviceLimits structure. If pname:maxMemoryAllocationCount is exceeded, fname:vkAllocateMemory will return ename:VK_ERROR_TOO_MANY_OBJECTS. [NOTE] .Note ==== Some platforms may: have a limit on the maximum size of a single allocation. For example, certain systems may: fail to create allocations with a size greater than or equal to 4GB. Such a limit is implementation-dependent, and if such a failure occurs then the error ename:VK_ERROR_OUT_OF_DEVICE_MEMORY should: be returned. ==== A memory object is freed by calling: include::../protos/vkFreeMemory.txt[] * pname:device is the logical device that owns the memory. * pname:memory is the sname:VkDeviceMemory object to be freed. * pname:pAllocator controls host memory allocation as described in the <> chapter. include::../validity/protos/vkFreeMemory.txt[] Before freeing a memory object, an application must: ensure the memory object is no longer in use by the device--for example by command buffers queued for execution. The memory can: remain bound to images or buffers at the time the memory object is freed, but any further use of them (on host or device) for anything other than destroying those objects will result in undefined behavior. If there are still any bound images or buffers, the memory may: not be immediately released by the implementation, but must: be released by the time all bound images and buffers have been destroyed. Once memory is released, it is returned to the heap from which it was allocated. How memory objects are bound to Images and Buffers is described in detail in the <> section. If a memory object is mapped at the time it is freed, it is implicitly unmapped. [[memory-device-hostaccess]] === Host Access to Device Memory Objects Memory objects created with fname:vkAllocateMemory are not directly host accessible. Memory objects created with the memory property ename:VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT are considered _mappable_. Memory objects must: be mappable in order to be successfully mapped on the host. An application retrieves a host virtual address pointer to a region of a mappable memory object by calling: include::../protos/vkMapMemory.txt[] * pname:device is the logical device that owns the memory. * pname:memory is the sname:VkDeviceMemory object to be mapped. * pname:offset is a zero-based byte offset from the beginning of the memory object. * pname:size is the size of the memory range to map, or ename:VK_WHOLE_SIZE to map from pname:offset to the end of the allocation. * pname:flags is reserved for future use, and must: be zero. * pname:ppData points to a pointer in which is returned a host-accessible pointer to the beginning of the mapped range. This pointer minus pname:offset must: be aligned to at least sname:VkPhysicalDeviceLimits::pname:minMemoryMapAlignment. include::../validity/protos/vkMapMemory.txt[] It is an application error to call fname:vkMapMemory on a memory object that is already mapped. ifdef::editing-notes[] [NOTE] .editing-note ==== TODO (Tobias) - There's a circular section reference in this next section. The information is all covered by both places, but it seems a bit weird to have them reference each other. Not sure how to resolve it. ==== endif::editing-notes[] [[memory-device-hostaccess-hazards]] fname:vkMapMemory does not check whether the device memory is currently in use before returning the host-accessible pointer. The application must: guarantee that any previously submitted command that writes to this range has completed before the host reads from or writes to that range, and that any previously submitted command that reads from that range has completed before the host writes to that region (see <> for details on fulfilling such a guarantee). If the device memory was allocated without the ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT set, these guarantees must: be made for an extended range: the application must: round down the start of the range to the nearest multiple of sname:VkPhysicalDeviceLimits::pname:nonCoherentAtomSize, and round the end of the range up to the nearest multiple of sname:VkPhysicalDeviceLimits::pname:nonCoherentAtomSize. While a range of device memory is mapped for host access, the application is responsible for synchronizing both device and host access to that memory range. [NOTE] .Note ==== It is important for the application developer to become meticulously familiar with all of the mechanisms described in the chapter on <> as they are crucial to maintaining memory access ordering. ==== Host-visible memory types that advertise the ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT property still require <> between host and device in order to be coherent, but do not require additional cache management operations (fname:vkFlushMappedMemoryRanges or fname:vkInvalidateMappedMemoryRanges) to achieve coherency. For host writes to be seen by subsequent command buffer operations, a pipeline barrier from a source of ename:VK_ACCESS_HOST_WRITE_BIT and ename:VK_PIPELINE_STAGE_HOST_BIT to a destination of the relevant device pipeline stages and access types must: be performed. Note that such a barrier is performed <> upon each command buffer submission, so an explicit barrier is only rarely needed (e.g. if a command buffer waits upon an event signaled by the host, where the host wrote some data after submission). For device writes to be seen by subsequent host reads, a pipeline barrier is required: to <>. In order to enable applications to work with non-coherent memory allocations, two entry points are provided. To flush host write caches, an application must: use fname:vkFlushMappedMemoryRanges, while fname:vkInvalidateMappedMemoryRanges allows invalidating host input caches so that device writes become visible to the host. fname:vkFlushMappedMemoryRanges must: be called after the host writes to non-coherent memory have completed and before command buffers that will read or write any of those memory locations are submitted to a queue. Similarly, fname:vkInvalidateMappedMemoryRanges must: be called after command buffers that execute and flush (via memory barriers) the device writes have completed, and before the host will read or write any of those locations. include::../protos/vkFlushMappedMemoryRanges.txt[] * pname:device is the logical device that owns the memory ranges. * pname:memoryRangeCount is the length of the pname:pMemoryRanges array. * pname:pMemoryRanges is a pointer to an array of slink:VkMappedMemoryRange structures describing the memory ranges to flush. include::../validity/protos/vkFlushMappedMemoryRanges.txt[] include::../protos/vkInvalidateMappedMemoryRanges.txt[] * pname:device is the logical device that owns the memory ranges. * pname:memoryRangeCount is the length of the pname:pMemoryRanges array. * pname:pMemoryRanges is a pointer to an array of slink:VkMappedMemoryRange structures describing the memory ranges to invalidate. include::../validity/protos/vkInvalidateMappedMemoryRanges.txt[] The sname:VkMappedMemoryRange structure is defined as: include::../structs/VkMappedMemoryRange.txt[] * pname:sType is the type of this structure. * pname:pNext is `NULL` or a pointer to an extension-specific structure. * pname:memory is the memory object to which this range belongs. * pname:offset is the zero-based byte offset from the beginning of the memory object. * pname:size is either the size of range, or ename:VK_WHOLE_SIZE to affect the range from pname:offset to the end of the current mapping of the allocation. include::../validity/structs/VkMappedMemoryRange.txt[] [NOTE] .Note ==== If the memory object was created with the ename:VK_MEMORY_PROPERTY_HOST_COHERENT_BIT set, fname:vkFlushMappedMemoryRanges and fname:vkInvalidateMappedMemoryRanges are unnecessary and may: have performance cost. ==== Once host access to a memory object is no longer needed by the application, it can: be unmapped by calling : include::../protos/vkUnmapMemory.txt[] * pname:device is the logical device that owns the memory. * pname:memory is the memory object to be unmapped. include::../validity/protos/vkUnmapMemory.txt[] [[memory-device-lazy_allocation]] === Lazily Allocated Memory If the memory object is allocated from a heap with the ename:VK_MEMORY_PROPERTY_LAZILY_ALLOCATED_BIT bit set, that object's backing memory may: be provided by the implementation lazily. The actual committed size of the memory may: initially be as small as zero (or as large as the requested size), and monotonically increases as additional memory is needed. A memory type with this flag set is only allowed to be bound to a sname:VkImage whose usage flags include ename:VK_IMAGE_USAGE_TRANSIENT_ATTACHMENT_BIT. [NOTE] .Note ==== Using lazily allocated memory objects for framebuffer attachments that are not needed once a render pass instance has completed may: allow some implementations to never allocate memory for such attachments. ==== Determining the amount of lazily-allocated memory that is currently committed for a memory object is achieved by calling: include::../protos/vkGetDeviceMemoryCommitment.txt[] * pname:device is the logical device that owns the memory. * pname:memory is the memory object being queried. * pname:pCommittedMemoryInBytes is a pointer to a basetype:VkDeviceSize value in which the number of bytes currently committed is returned, on success. include::../validity/protos/vkGetDeviceMemoryCommitment.txt[] The implementation may: update the commitment at any time, and the value returned by this query may: be out of date. The implementation guarantees to allocate any committed memory from the heapIndex indicated by the memory type that the memory object was created with.