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| <div class="title">Custom memory pools </div> </div> |
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| <div class="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> |
| <ul> |
| <li>Keep certain kind of allocations separate from others.</li> |
| <li>Enforce particular, fixed size of Vulkan memory blocks.</li> |
| <li>Limit maximum amount of Vulkan memory allocated for that pool.</li> |
| <li>Reserve minimum or fixed amount of Vulkan memory always preallocated for that pool.</li> |
| </ul> |
| <p>To use custom memory pools:</p> |
| <ol type="1"> |
| <li>Fill <a class="el" href="struct_vma_pool_create_info.html" title="Describes parameter of created VmaPool. ">VmaPoolCreateInfo</a> structure.</li> |
| <li>Call <a class="el" href="vk__mem__alloc_8h.html#a5c8770ded7c59c8caac6de0c2cb00b50" title="Allocates Vulkan device memory and creates VmaPool object. ">vmaCreatePool()</a> to obtain <code>VmaPool</code> handle.</li> |
| <li>When making an allocation, set <a class="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 usage.</li> |
| </ol> |
| <p>Example:</p> |
| <div class="fragment"><div class="line"><span class="comment">// Create a pool that can have at most 2 blocks, 128 MiB each.</span></div><div class="line"><a class="code" href="struct_vma_pool_create_info.html">VmaPoolCreateInfo</a> poolCreateInfo = {};</div><div class="line">poolCreateInfo.<a class="code" href="struct_vma_pool_create_info.html#a596fa76b685d3f1f688f84a709a5b319">memoryTypeIndex</a> = ...</div><div class="line">poolCreateInfo.blockSize = 128ull * 1024 * 1024;</div><div class="line">poolCreateInfo.<a class="code" href="struct_vma_pool_create_info.html#ae41142f2834fcdc82baa4883c187b75c">maxBlockCount</a> = 2;</div><div class="line"></div><div class="line">VmaPool pool;</div><div class="line"><a class="code" href="vk__mem__alloc_8h.html#a5c8770ded7c59c8caac6de0c2cb00b50">vmaCreatePool</a>(allocator, &poolCreateInfo, &pool);</div><div class="line"></div><div class="line"><span class="comment">// Allocate a buffer out of it.</span></div><div class="line">VkBufferCreateInfo bufCreateInfo = { VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO };</div><div class="line">bufCreateInfo.size = 1024;</div><div class="line">bufCreateInfo.usage = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT;</div><div class="line"></div><div class="line"><a class="code" href="struct_vma_allocation_create_info.html">VmaAllocationCreateInfo</a> allocCreateInfo = {};</div><div class="line">allocCreateInfo.<a class="code" href="struct_vma_allocation_create_info.html#a6272c0555cfd1fe28bff1afeb6190150">pool</a> = pool;</div><div class="line"></div><div class="line">VkBuffer buf;</div><div class="line">VmaAllocation alloc;</div><div class="line"><a class="code" href="struct_vma_allocation_info.html">VmaAllocationInfo</a> allocInfo;</div><div class="line"><a class="code" href="vk__mem__alloc_8h.html#ac72ee55598617e8eecca384e746bab51">vmaCreateBuffer</a>(allocator, &bufCreateInfo, &allocCreateInfo, &buf, &alloc, &allocInfo);</div></div><!-- fragment --><p>You have to free all allocations made from this pool before destroying it.</p> |
| <div class="fragment"><div class="line"><a class="code" href="vk__mem__alloc_8h.html#a0d9f4e4ba5bf9aab1f1c746387753d77">vmaDestroyBuffer</a>(allocator, buf, alloc);</div><div class="line"><a class="code" href="vk__mem__alloc_8h.html#a5485779c8f1948238fc4e92232fa65e1">vmaDestroyPool</a>(allocator, pool);</div></div><!-- fragment --><h1><a class="anchor" id="custom_memory_pools_MemTypeIndex"></a> |
| Choosing memory type index</h1> |
| <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 code similar to the following:</p> |
| <div class="fragment"><div class="line">VkBufferCreateInfo dummyBufCreateInfo = { VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO };</div><div class="line">dummyBufCreateInfo.size = 1024; <span class="comment">// Whatever.</span></div><div class="line">dummyBufCreateInfo.usage = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT; <span class="comment">// Change if needed.</span></div><div class="line"></div><div class="line">VkBuffer dummyBuf;</div><div class="line">vkCreateBuffer(device, &dummyBufCreateInfo, <span class="keyword">nullptr</span>, &dummyBuf);</div><div class="line"></div><div class="line">VkMemoryRequirements memReq;</div><div class="line">vkGetBufferMemoryRequirements(device, dummyBuf, &memReq);</div><div class="line"></div><div class="line"><a class="code" href="struct_vma_allocation_create_info.html">VmaAllocationCreateInfo</a> allocCreateInfo = {};</div><div class="line">allocCreateInfo.<a class="code" href="struct_vma_allocation_create_info.html#accb8b06b1f677d858cb9af20705fa910">usage</a> = <a class="code" href="vk__mem__alloc_8h.html#aa5846affa1e9da3800e3e78fae2305ccac6b5dc1432d88647aa4cd456246eadf7">VMA_MEMORY_USAGE_GPU_ONLY</a>; <span class="comment">// Change if needed.</span></div><div class="line"></div><div class="line">uint32_t memTypeIndex;</div><div class="line"><a class="code" href="vk__mem__alloc_8h.html#aef15a94b58fbcb0fe706d5720e84a74a">vmaFindMemoryTypeIndex</a>(allocator, memReq.memoryTypeBits, &allocCreateInfo, &memTypeIndex);</div><div class="line"></div><div class="line">vkDestroyBuffer(device, dummyBuf, <span class="keyword">nullptr</span>);</div><div class="line"></div><div class="line"><a class="code" href="struct_vma_pool_create_info.html">VmaPoolCreateInfo</a> poolCreateInfo = {};</div><div class="line">poolCreateInfo.<a class="code" href="struct_vma_pool_create_info.html#a596fa76b685d3f1f688f84a709a5b319">memoryTypeIndex</a> = memTypeIndex;</div><div class="line"><span class="comment">// ...</span></div></div><!-- fragment --><p>Dummy buffer is needed to query driver for <code>memReq.memoryTypeBits</code>. Memory is never allocated for this buffer. You should fill structures <code>dummyBufCreateInfo</code> and <code>allocCreateInfo</code> with the same parameters as you are going to use for buffers created in your pool. </p> |
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