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Made virtual allocations not applying VMA_DEBUG_MARGIN

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Improved and regenerated documentation.
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Adam Sawicki 2021-10-30 23:29:01 +02:00
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@ -151,7 +151,7 @@ Linear allocation algorithm</h1>
<p ><img src="../gfx/Linear_allocator_1_algo_default.png" alt="Default allocation algorithm" class="inline"/></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 <a class="el" href="vk__mem__alloc_8h.html#a9a7c45f9c863695d98c83fa5ac940fe7a13c8a444197c67866be9cb05599fc726" title="Enables alternative, linear allocation algorithm in this pool.">VMA_POOL_CREATE_LINEAR_ALGORITHM_BIT</a> to <a class="el" href="struct_vma_pool_create_info.html#a8405139f63d078340ae74513a59f5446" title="Use combination of VmaPoolCreateFlagBits.">VmaPoolCreateInfo::flags</a> while creating <a class="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 ><img src="../gfx/Linear_allocator_2_algo_linear.png" alt="Linear allocation algorithm" class="inline"/></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.</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>
<h2><a class="anchor" id="linear_algorithm_free_at_once"></a>
Free-at-once</h2>
<p >In a pool that uses linear algorithm, you still need to free all the allocations individually, e.g. by using <a class="el" href="vk__mem__alloc_8h.html#a5fea5518972ae9094b1526cbcb19b05f" title="Frees memory previously allocated using vmaAllocateMemory(), vmaAllocateMemoryForBuffer(),...">vmaFreeMemory()</a> or <a class="el" href="vk__mem__alloc_8h.html#a0d9f4e4ba5bf9aab1f1c746387753d77" 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>
@ -169,7 +169,7 @@ Double stack</h2>
<li>First, default one, growing up from offset 0.</li>
<li>Second, "upper" one, growing down from the end towards lower offsets.</li>
</ul>
<p >To make allocation from upper stack, add flag <a class="el" href="vk__mem__alloc_8h.html#ad9889c10c798b040d59c92f257cae597a42ba3a2d2c7117953210b7c3ef8da0df">VMA_ALLOCATION_CREATE_UPPER_ADDRESS_BIT</a> to <a class="el" href="struct_vma_allocation_create_info.html#add09658ac14fe290ace25470ddd6d41b" title="Use VmaAllocationCreateFlagBits enum.">VmaAllocationCreateInfo::flags</a>.</p>
<p >To make allocation from the upper stack, add flag <a class="el" href="vk__mem__alloc_8h.html#ad9889c10c798b040d59c92f257cae597a42ba3a2d2c7117953210b7c3ef8da0df">VMA_ALLOCATION_CREATE_UPPER_ADDRESS_BIT</a> to <a class="el" href="struct_vma_allocation_create_info.html#add09658ac14fe290ace25470ddd6d41b" title="Use VmaAllocationCreateFlagBits enum.">VmaAllocationCreateInfo::flags</a>.</p>
<p ><img src="../gfx/Linear_allocator_7_double_stack.png" alt="Double stack" class="inline"/></p>
<p >Double stack is available only in pools with one memory block - <a class="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>
@ -182,10 +182,9 @@ Ring buffer</h2>
<p >Ring buffer is available only in pools with one memory block - <a class="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>
<h1><a class="anchor" id="buddy_algorithm"></a>
Buddy allocation algorithm</h1>
<p >There is another allocation algorithm that can be used with custom pools, called "buddy". Its internal data structure is based on a tree of blocks, each having size that is a power of two and a half of its parent's size. When you want to allocate memory of certain size, a free node in the tree is located. If it is too large, it is recursively split into two halves (called "buddies"). However, if requested allocation size is not a power of two, the size of a tree node is aligned up to the nearest power of two and the remaining space is wasted. When two buddy nodes become free, they are merged back into one larger node.</p>
<p >There is another allocation algorithm that can be used with custom pools, called "buddy". Its internal data structure is based on a binary tree of blocks, each having size that is a power of two and a half of its parent's size. When you want to allocate memory of certain size, a free node in the tree is located. If it is too large, it is recursively split into two halves (called "buddies"). However, if requested allocation size is not a power of two, the size of the allocation is aligned up to the nearest power of two and the remaining space is wasted. When two buddy nodes become free, they are merged back into one larger node.</p>
<p ><img src="../gfx/Buddy_allocator.png" alt="Buddy allocator" class="inline"/></p>
<p >The advantage of buddy allocation algorithm over default algorithm is faster allocation and deallocation, as well as smaller external fragmentation. The disadvantage is more wasted space (internal fragmentation).</p>
<p >For more information, please search the Internet for "Buddy memory allocation" - sources that describe this concept in general.</p>
<p >The advantage of buddy allocation algorithm over default algorithm is faster allocation and deallocation, as well as smaller external fragmentation. The disadvantage is more wasted space (internal fragmentation). For more information, please search the Internet for "Buddy memory allocation" - sources that describe this concept in general.</p>
<p >To use buddy allocation algorithm with a custom pool, add flag <a class="el" href="vk__mem__alloc_8h.html#a9a7c45f9c863695d98c83fa5ac940fe7a97a0dc38e5161b780594d998d313d35e" title="Enables alternative, buddy allocation algorithm in this pool.">VMA_POOL_CREATE_BUDDY_ALGORITHM_BIT</a> to <a class="el" href="struct_vma_pool_create_info.html#a8405139f63d078340ae74513a59f5446" title="Use combination of VmaPoolCreateFlagBits.">VmaPoolCreateInfo::flags</a> while creating <a class="el" href="struct_vma_pool.html" title="Represents custom memory pool.">VmaPool</a> object.</p>
<p >Several limitations apply to pools that use buddy algorithm:</p>
<ul>