Allocation user data

You can annotate allocations with your own information, e.g. for debugging purposes. To do that, fill VmaAllocationCreateInfo::pUserData field when creating an allocation. It is an opaque void* pointer. You can use it e.g. as a pointer, some handle, index, key, ordinal number or any other value that would associate the allocation with your custom metadata.

VkBufferCreateInfo bufCreateInfo = ...
 
MyBufferMetadata* pMetadata = CreateBufferMetadata();
 
VmaAllocationCreateInfo allocCreateInfo = {};
allocCreateInfo.usage = VMA_MEMORY_USAGE_AUTO;
allocCreateInfo.pUserData = pMetadata;
 
VkBuffer buffer;
VmaAllocation allocation;
vmaCreateBuffer(allocator, &bufCreateInfo, &allocCreateInfo, &buffer, &allocation, nullptr);

The pointer may be later retrieved as VmaAllocationInfo::pUserData:

VmaAllocationInfo allocInfo;
vmaGetAllocationInfo(allocator, allocation, &allocInfo);
MyBufferMetadata* pMetadata = (MyBufferMetadata*)allocInfo.pUserData;

It can also be changed using function vmaSetAllocationUserData().

Values of (non-zero) allocations' pUserData are printed in JSON report created by vmaBuildStatsString() in hexadecimal form.

Allocation names

There is alternative mode available where pUserData pointer is used to point to a null-terminated string, giving a name to the allocation. To use this mode, set VMA_ALLOCATION_CREATE_USER_DATA_COPY_STRING_BIT flag in VmaAllocationCreateInfo::flags. Then pUserData passed as VmaAllocationCreateInfo::pUserData or argument to vmaSetAllocationUserData() must be either null or a pointer to a null-terminated string. The library creates internal copy of the string, so the pointer you pass doesn't need to be valid for whole lifetime of the allocation. You can free it after the call.

VkImageCreateInfo imageInfo = ...
 
std::string imageName = "Texture: ";
imageName += fileName;
 
VmaAllocationCreateInfo allocCreateInfo = {};
allocCreateInfo.usage = VMA_MEMORY_USAGE_AUTO;
allocCreateInfo.flags = VMA_ALLOCATION_CREATE_USER_DATA_COPY_STRING_BIT;
allocCreateInfo.pUserData = imageName.c_str();
 
VkImage image;
VmaAllocation allocation;
vmaCreateImage(allocator, &imageInfo, &allocCreateInfo, &image, &allocation, nullptr);

The value of pUserData pointer of the allocation will be different than the one you passed when setting allocation's name - pointing to a buffer managed internally that holds copy of the string.

VmaAllocationInfo allocInfo;
vmaGetAllocationInfo(allocator, allocation, &allocInfo);
const char* imageName = (const char*)allocInfo.pUserData;
printf("Image name: %s\n", imageName);

That string is also printed in JSON report created by vmaBuildStatsString().

Note: Passing string name to VMA allocation doesn't automatically set it to the Vulkan buffer or image created with it. You must do it manually using an extension like VK_EXT_debug_utils, which is independent of this library.