diff --git a/src/vk_mem_alloc.h b/src/vk_mem_alloc.h index a7df731..fc504ba 100644 --- a/src/vk_mem_alloc.h +++ b/src/vk_mem_alloc.h @@ -1,5 +1,4 @@ // -// // Copyright (c) 2017-2019 Advanced Micro Devices, Inc. All rights reserved. // // Permission is hereby granted, free of charge, to any person obtaining a copy @@ -30,9 +29,9 @@ extern "C" { /** \mainpage Vulkan Memory Allocator -Version 2.3.0-development (2019-07-02) +Version 2.3.0-development (2019-11-02) -Copyright (c) 2017-2018 Advanced Micro Devices, Inc. All rights reserved. \n +Copyright (c) 2017-2019 Advanced Micro Devices, Inc. All rights reserved. \n License: MIT Documentation of all members: vk_mem_alloc.h @@ -55,6 +54,9 @@ Documentation of all members: vk_mem_alloc.h - [Persistently mapped memory](@ref memory_mapping_persistently_mapped_memory) - [Cache control](@ref memory_mapping_cache_control) - [Finding out if memory is mappable](@ref memory_mapping_finding_if_memory_mappable) + - \subpage staying_within_budget + - [Querying for budget](@ref staying_within_budget_querying_for_budget) + - [Controlling memory usage](@ref staying_within_budget_controlling_memory_usage) - \subpage custom_memory_pools - [Choosing memory type index](@ref custom_memory_pools_MemTypeIndex) - [Linear allocation algorithm](@ref linear_algorithm) @@ -524,6 +526,78 @@ else \endcode +\page staying_within_budget Staying within budget + +When developing a graphics-intensive game or program, it is important to avoid allocating +more GPU memory than it's physically available. When the memory is over-committed, +various bad things can happen, depending on the specific GPU, graphics driver, and +operating system: + +- It may just work without any problems. +- The application may slow down because some memory blocks are moved to system RAM + and the GPU has to access them through PCI Express bus. +- A new allocation may take very long time to complete, even few seconds, and possibly + freeze entire system. +- The new allocation may fail with `VK_ERROR_OUT_OF_DEVICE_MEMORY`. +- It may even result in GPU crash (TDR), observed as `VK_ERROR_DEVICE_LOST` + returned somewhere later. + +\section staying_within_budget_querying_for_budget Querying for budget + +To query for current memory usage and available budget, use function vmaGetBudget(). +Returned structure #VmaBudget contains quantities expressed in bytes, per Vulkan memory heap. + +Please note that this function returns different information and works faster than +vmaCalculateStats(). vmaGetBudget() can be called every frame or even before every +allocation, while vmaCalculateStats() is intended to be used rarely, +only to obtain statistical information, e.g. for debugging purposes. + +It is recommended to use VK_EXT_memory_budget device extension to obtain information +about the budget from Vulkan device. VMA is able to use this extension automatically. +When not enabled, the allocator behaves same way, but then it estimates current usage +and available budget based on its internal information and Vulkan memory heap sizes, +which may be less precise. In order to use this extension: + +1. Make sure extensions VK_EXT_memory_budget and VK_KHR_get_physical_device_properties2 + required by it are available and enable them. Please note that the first is a device + extension and the second is instance extension! +2. Use flag #VMA_ALLOCATOR_CREATE_ ?? when creating #VmaAllocator object. +3. Make sure to call vmaSetCurrentFrameIndex() every frame. Budget is queried from + Vulkan inside of it to avoid overhead of querying it with every allocation. + +\section staying_within_budget_controlling_memory_usage Controlling memory usage + +There are many ways in which you can try to stay within the budget. + +First, when making new allocation requires allocating a new memory block, the library +tries not to exceed the budget automatically. If a block with default recommended size +(e.g. 256 MB) would go over budget, a smaller block is allocated, possibly even +dedicated memory for just this resource. + +If the size of the requested resource plus current memory usage is more than the +budget, by default the library still tries to create it, leaving it to the Vulkan +implementation whether the allocation succeeds or fails. You can change this behavior +by using #VMA_ALLOCATION_CREATE_WITHIN_BUDGET_BIT flag. With it, the allocation is +not made if it would exceed the budget or if the budget is already exceeded. +Some other allocations become lost instead to make room for it, if the mechanism of +[lost allocations](@ref lost_allocations) is used. +If that is not possible, the allocation fails with `VK_ERROR_OUT_OF_DEVICE_MEMORY`. +Example usage pattern may be to pass the #VMA_ALLOCATION_CREATE_WITHIN_BUDGET_BIT flag +when creating resources that are not essential for the application (e.g. the texture +of a specific object) and not to pass it when creating critically important resources +(e.g. render targets). + +Finally, you can also use #VMA_ALLOCATION_CREATE_NEVER_ALLOCATE_BIT flag to make sure +a new allocation is created only when it fits inside one of the existing memory blocks. +If it would require to allocate a new block, if fails instead with `VK_ERROR_OUT_OF_DEVICE_MEMORY`. +This also ensures that the function call is very fast because it never goes to Vulkan +to obtain a new block. + +Please note that creating \ref custom_memory_pools with VmaPoolCreateInfo::minBlockCount +set to more than 0 will try to allocate memory blocks without checking whether they +fit within budget. + + \page custom_memory_pools Custom memory pools A memory pool contains a number of `VkDeviceMemory` blocks. @@ -2102,17 +2176,10 @@ typedef struct VmaBudget It might be different (most probably smaller) than `VkMemoryHeap::size[heapIndex]` due to factors external to the program, like other programs also consuming system resources. - Difference `budget - usage` is the amount of additional memory that can probably - be allocated without problems. Exceeding the budget may result, depending on operating - system and graphics driver: - - - Allocation failing with `VK_ERROR_OUT_OF_DEVICE_MEMORY`. - - Allocation taking very long time, even few seconds. - - Overall system slowdown. - - Even GPU crash (TDR), observed as `VK_ERROR_DEVICE_LOST` returned somewhere later. + be allocated without problems. Exceeding the budget may result in various problems. */ - VkDeviceSize budget; + VkDeviceSize budget[VK_MAX_MEMORY_HEAPS]; } VmaBudget; /** \brief Retrieves information about current memory budget for all memory heaps.