<divclass="textblock"><p>A memory pool contains a number of <code>VkDeviceMemory</code> 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.</p>
<p>You can create custom pool and allocate memory out of it. It can be useful if you want to:</p>
<li>Use extra parameters for a set of your allocations that are available in <aclass="el"href="struct_vma_pool_create_info.html"title="Describes parameter of created VmaPool.">VmaPoolCreateInfo</a> but not in <aclass="el"href="struct_vma_allocation_create_info.html">VmaAllocationCreateInfo</a> - e.g., custom minimum alignment, custom <code>pNext</code> chain.</li>
<li>When making an allocation, set <aclass="el"href="struct_vma_allocation_create_info.html#a6272c0555cfd1fe28bff1afeb6190150"title="Pool that this allocation should be created in.">VmaAllocationCreateInfo::pool</a> to this handle. You don't need to specify any other parameters of this structure, like <code>usage</code>.</li>
<divclass="ttc"id="astruct_vma_allocation_create_info_html_a6272c0555cfd1fe28bff1afeb6190150"><divclass="ttname"><ahref="struct_vma_allocation_create_info.html#a6272c0555cfd1fe28bff1afeb6190150">VmaAllocationCreateInfo::pool</a></div><divclass="ttdeci">VmaPool pool</div><divclass="ttdoc">Pool that this allocation should be created in.</div><divclass="ttdef"><b>Definition:</b> vk_mem_alloc.h:1244</div></div>
<divclass="ttc"id="astruct_vma_allocation_html"><divclass="ttname"><ahref="struct_vma_allocation.html">VmaAllocation</a></div><divclass="ttdoc">Represents single memory allocation.</div></div>
<divclass="ttc"id="astruct_vma_allocation_info_html"><divclass="ttname"><ahref="struct_vma_allocation_info.html">VmaAllocationInfo</a></div><divclass="ttdoc">Parameters of VmaAllocation objects, that can be retrieved using function vmaGetAllocationInfo().</div><divclass="ttdef"><b>Definition:</b> vk_mem_alloc.h:1327</div></div>
<divclass="ttc"id="astruct_vma_pool_create_info_html"><divclass="ttname"><ahref="struct_vma_pool_create_info.html">VmaPoolCreateInfo</a></div><divclass="ttdoc">Describes parameter of created VmaPool.</div><divclass="ttdef"><b>Definition:</b> vk_mem_alloc.h:1263</div></div>
<divclass="ttc"id="astruct_vma_pool_create_info_html_a596fa76b685d3f1f688f84a709a5b319"><divclass="ttname"><ahref="struct_vma_pool_create_info.html#a596fa76b685d3f1f688f84a709a5b319">VmaPoolCreateInfo::memoryTypeIndex</a></div><divclass="ttdeci">uint32_t memoryTypeIndex</div><divclass="ttdoc">Vulkan memory type index to allocate this pool from.</div><divclass="ttdef"><b>Definition:</b> vk_mem_alloc.h:1266</div></div>
<divclass="ttc"id="astruct_vma_pool_create_info_html_ae41142f2834fcdc82baa4883c187b75c"><divclass="ttname"><ahref="struct_vma_pool_create_info.html#ae41142f2834fcdc82baa4883c187b75c">VmaPoolCreateInfo::maxBlockCount</a></div><divclass="ttdeci">size_t maxBlockCount</div><divclass="ttdoc">Maximum number of blocks that can be allocated in this pool. Optional.</div><divclass="ttdef"><b>Definition:</b> vk_mem_alloc.h:1292</div></div>
</div><!-- fragment --><p>New versions of this library support creating dedicated allocations in custom pools. It is supported only when <aclass="el"href="struct_vma_pool_create_info.html#aa4265160536cdb9be821b7686c16c676"title="Size of a single VkDeviceMemory block to be allocated as part of this pool, in bytes....">VmaPoolCreateInfo::blockSize</a> = 0. To use this feature, set <aclass="el"href="struct_vma_allocation_create_info.html#a6272c0555cfd1fe28bff1afeb6190150"title="Pool that this allocation should be created in.">VmaAllocationCreateInfo::pool</a> to the pointer to your custom pool and <aclass="el"href="struct_vma_allocation_create_info.html#add09658ac14fe290ace25470ddd6d41b"title="Use VmaAllocationCreateFlagBits enum.">VmaAllocationCreateInfo::flags</a> to <aclass="el"href="group__group__alloc.html#ggad9889c10c798b040d59c92f257cae597a3fc311d855c2ff53f1090ef5c722b38f"title="Set this flag if the allocation should have its own memory block.">VMA_ALLOCATION_CREATE_DEDICATED_MEMORY_BIT</a>.</p>
<dlclass="section note"><dt>Note</dt><dd>Excessive use of custom pools is a common mistake when using this library. Custom pools may be useful for special purposes - when you want to keep certain type of resources separate e.g. to reserve minimum amount of memory for them or limit maximum amount of memory they can occupy. For most resources this is not needed and so it is not recommended to create <aclass="el"href="struct_vma_pool.html"title="Represents custom memory pool.">VmaPool</a> objects and allocations out of them. Allocating from the default pool is sufficient.</dd></dl>
<p>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 <aclass="el"href="group__group__alloc.html#gae790ab9ffaf7667fb8f62523e6897888"title="Helps to find memoryTypeIndex, given VkBufferCreateInfo and VmaAllocationCreateInfo.">vmaFindMemoryTypeIndexForBufferInfo()</a>, <aclass="el"href="group__group__alloc.html#ga088da83d8eaf3ce9056d9ea0b981d472"title="Helps to find memoryTypeIndex, given VkImageCreateInfo and VmaAllocationCreateInfo.">vmaFindMemoryTypeIndexForImageInfo()</a>. You need to provide structures with example parameters of buffers or images that you are going to create in that pool.</p>
<li><code>VkBufferCreateInfo</code>: 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 <code>VK_BUFFER_USAGE_</code> flags may work, but you shouldn't create images in a pool intended for buffers or the other way around.</li>
<li><aclass="el"href="struct_vma_allocation_create_info.html">VmaAllocationCreateInfo</a>: You don't need to pass same parameters. Fill only <code>pool</code> member. Other members are ignored anyway.</li>
<p>Each Vulkan memory block managed by this library has accompanying metadata that keeps track of used and unused regions. By default, the metadata structure and algorithm tries to find best place for new allocations among free regions to optimize memory usage. This way you can allocate and free objects in any order.</p>
<p>Sometimes there is a need to use simpler, linear allocation algorithm. You can create custom pool that uses such algorithm by adding flag <aclass="el"href="group__group__alloc.html#gga9a7c45f9c863695d98c83fa5ac940fe7a13c8a444197c67866be9cb05599fc726"title="Enables alternative, linear allocation algorithm in this pool.">VMA_POOL_CREATE_LINEAR_ALGORITHM_BIT</a> to <aclass="el"href="struct_vma_pool_create_info.html#a8405139f63d078340ae74513a59f5446"title="Use combination of VmaPoolCreateFlagBits.">VmaPoolCreateInfo::flags</a> while creating <aclass="el"href="struct_vma_pool.html"title="Represents custom memory pool.">VmaPool</a> object. Then an alternative metadata management is used. It always creates new allocations after last one and doesn't reuse free regions after allocations freed in the middle. It results in better allocation performance and less memory consumed by metadata.</p>
<p>With this one flag, you can create a custom pool that can be used in many ways: free-at-once, stack, double stack, and ring buffer. See below for details. You don't need to specify explicitly which of these options you are going to use - it is detected automatically.</p>
<p>In a pool that uses linear algorithm, you still need to free all the allocations individually, e.g. by using <aclass="el"href="group__group__alloc.html#ga5fea5518972ae9094b1526cbcb19b05f"title="Frees memory previously allocated using vmaAllocateMemory(), vmaAllocateMemoryForBuffer(),...">vmaFreeMemory()</a> or <aclass="el"href="group__group__alloc.html#ga0d9f4e4ba5bf9aab1f1c746387753d77"title="Destroys Vulkan buffer and frees allocated memory.">vmaDestroyBuffer()</a>. You can free them in any order. New allocations are always made after last one - free space in the middle is not reused. However, when you release all the allocation and the pool becomes empty, allocation starts from the beginning again. This way you can use linear algorithm to speed up creation of allocations that you are going to release all at once.</p>
<p>This mode is also available for pools created with <aclass="el"href="struct_vma_pool_create_info.html#ae41142f2834fcdc82baa4883c187b75c"title="Maximum number of blocks that can be allocated in this pool. Optional.">VmaPoolCreateInfo::maxBlockCount</a> value that allows multiple memory blocks.</p>
<p>When you free an allocation that was created last, its space can be reused. Thanks to this, if you always release allocations in the order opposite to their creation (LIFO - Last In First Out), you can achieve behavior of a stack.</p>
<p>This mode is also available for pools created with <aclass="el"href="struct_vma_pool_create_info.html#ae41142f2834fcdc82baa4883c187b75c"title="Maximum number of blocks that can be allocated in this pool. Optional.">VmaPoolCreateInfo::maxBlockCount</a> value that allows multiple memory blocks.</p>
<p>To make allocation from the upper stack, add flag <aclass="el"href="group__group__alloc.html#ggad9889c10c798b040d59c92f257cae597a42ba3a2d2c7117953210b7c3ef8da0df">VMA_ALLOCATION_CREATE_UPPER_ADDRESS_BIT</a> to <aclass="el"href="struct_vma_allocation_create_info.html#add09658ac14fe290ace25470ddd6d41b"title="Use VmaAllocationCreateFlagBits enum.">VmaAllocationCreateInfo::flags</a>.</p>
<p>Double stack is available only in pools with one memory block - <aclass="el"href="struct_vma_pool_create_info.html#ae41142f2834fcdc82baa4883c187b75c"title="Maximum number of blocks that can be allocated in this pool. Optional.">VmaPoolCreateInfo::maxBlockCount</a> must be 1. Otherwise behavior is undefined.</p>
<p>When the two stacks' ends meet so there is not enough space between them for a new allocation, such allocation fails with usual <code>VK_ERROR_OUT_OF_DEVICE_MEMORY</code> error.</p>
<p>When you free some allocations from the beginning and there is not enough free space for a new one at the end of a pool, allocator's "cursor" wraps around to the beginning and starts allocation there. Thanks to this, if you always release allocations in the same order as you created them (FIFO - First In First Out), you can achieve behavior of a ring buffer / queue.</p>
<p>Ring buffer is available only in pools with one memory block - <aclass="el"href="struct_vma_pool_create_info.html#ae41142f2834fcdc82baa4883c187b75c"title="Maximum number of blocks that can be allocated in this pool. Optional.">VmaPoolCreateInfo::maxBlockCount</a> must be 1. Otherwise behavior is undefined.</p>
<dlclass="section note"><dt>Note</dt><dd><aclass="el"href="defragmentation.html">Defragmentation</a> is not supported in custom pools created with <aclass="el"href="group__group__alloc.html#gga9a7c45f9c863695d98c83fa5ac940fe7a13c8a444197c67866be9cb05599fc726"title="Enables alternative, linear allocation algorithm in this pool.">VMA_POOL_CREATE_LINEAR_ALGORITHM_BIT</a>. </dd></dl>
