Custom memory pools

A memory pool contains a number of VkDeviceMemory blocks. The library automatically creates and manages default pool for each memory type available on the device. Default memory pool automatically grows in size. Size of allocated blocks is also variable and managed automatically.

You can create custom pool and allocate memory out of it. It can be useful if you want to:

• Keep certain kind of allocations separate from others.
• Enforce particular, fixed size of Vulkan memory blocks.
• Limit maximum amount of Vulkan memory allocated for that pool.
• Reserve minimum or fixed amount of Vulkan memory always preallocated for that pool.

To use custom memory pools:

1. Fill VmaPoolCreateInfo structure.
2. Call vmaCreatePool() to obtain VmaPool handle.
3. When making an allocation, set VmaAllocationCreateInfo::pool to this handle. You don't need to specify any other parameters of this structure, like usage.

Example:

// Create a pool that can have at most 2 blocks, 128 MiB each.
VmaPoolCreateInfo poolCreateInfo = {};
poolCreateInfo.memoryTypeIndex = ...
poolCreateInfo.blockSize = 128ull * 1024 * 1024;
poolCreateInfo.maxBlockCount = 2;

VmaPool pool;
vmaCreatePool(allocator, &poolCreateInfo, &pool);

// Allocate a buffer out of it.
VkBufferCreateInfo bufCreateInfo = { VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO };
bufCreateInfo.size = 1024;
bufCreateInfo.usage = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT;

VmaAllocationCreateInfo allocCreateInfo = {};
allocCreateInfo.pool = pool;

VkBuffer buf;
VmaAllocation alloc;
VmaAllocationInfo allocInfo;
vmaCreateBuffer(allocator, &bufCreateInfo, &allocCreateInfo, &buf, &alloc, &allocInfo);

You have to free all allocations made from this pool before destroying it.

vmaDestroyBuffer(allocator, buf, alloc);
vmaDestroyPool(allocator, pool);

Choosing memory type index

When creating a pool, you must explicitly specify memory type index. To find the one suitable for your buffers or images, you can use helper functions vmaFindMemoryTypeIndexForBufferInfo(), vmaFindMemoryTypeIndexForImageInfo(). You need to provide structures with example parameters of buffers or images that you are going to create in that pool.

VkBufferCreateInfo exampleBufCreateInfo = { VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO };
exampleBufCreateInfo.size = 1024; // Whatever.
exampleBufCreateInfo.usage = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT; // Change if needed.

VmaAllocationCreateInfo allocCreateInfo = {};
allocCreateInfo.usage = VMA_MEMORY_USAGE_GPU_ONLY; // Change if needed.

uint32_t memTypeIndex;
vmaFindMemoryTypeIndexForBufferInfo(allocator, &exampleBufCreateInfo, &allocCreateInfo, &memTypeIndex);

VmaPoolCreateInfo poolCreateInfo = {};
poolCreateInfo.memoryTypeIndex = memTypeIndex;
// ...

When creating buffers/images allocated in that pool, provide following parameters:

• VkBufferCreateInfo: Prefer to pass same parameters as above. Otherwise you risk creating resources in a memory type that is not suitable for them, which may result in undefined behavior. Using different VK_BUFFER_USAGE_ flags may work, but you shouldn't create images in a pool intended for buffers or the other way around.
• VmaAllocationCreateInfo: You don't need to pass same parameters. Fill only pool member. Other members are ignored anyway.