VMA如何告诉库使用更大的2堆？

Question

在我当前的系统中，vulkan信息返回以下设备规范：

    memoryHeaps[0]:
        size   = 8589934592 (0x200000000) (8.00 GiB)
        budget = 7826571264 (0x1d2800000) (7.29 GiB)
        usage  = 0 (0x00000000) (0.00 B)
        flags: count = 1
            MEMORY_HEAP_DEVICE_LOCAL_BIT
    memoryHeaps[1]:
        size   = 12453414912 (0x2e6480800) (11.60 GiB)
        budget = 12453414912 (0x2e6480800) (11.60 GiB)
        usage  = 0 (0x00000000) (0.00 B)
        flags:
            None
    memoryHeaps[2]:
        size   = 257949696 (0x0f600000) (246.00 MiB)
        budget = 251068416 (0x0ef70000) (239.44 MiB)
        usage  = 6881280 (0x00690000) (6.56 MiB)
        flags: count = 1
            MEMORY_HEAP_DEVICE_LOCAL_BIT

总之，堆0好，堆2坏。

我收到的信息是，我分配的大量纹理耗尽了内存：

Message: Validation Error: [ VUID-vkAllocateMemory-pAllocateInfo-01713 ] Object 0: handle = 0x5562fe1c6760, name = Logical device: NVIDIA GeForce GTX 1070, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0xe9a2b96f | vkAllocateMemory: attempting to allocate 268435456 bytes from heap 2,but size of that heap is only 257949696 bytes. The Vulkan spec states: pAllocateInfo->allocationSize must be less than or equal to VkPhysicalDeviceMemoryProperties::memoryHeaps[memindex].size where memindex = VkPhysicalDeviceMemoryProperties::memoryTypes[pAllocateInfo->memoryTypeIndex].heapIndex as returned by vkGetPhysicalDeviceMemoryProperties for the VkPhysicalDevice that device was created from (https://vulkan.lunarg.com/doc/view/1.3.211.0/linux/1.3-extensions/vkspec.html#VUID-vkAllocateMemory-pAllocateInfo-01713)
Severity: VK_DEBUG_UTILS_MESSAGE_SEVERITY_ERROR_BIT_EXT

所以我想告诉VMA使用堆0，它确实有足够的容量来保持我的giga纹理。

我尝试这样分配：

vk::Device& device = h_interface->GetDevice();

    const bool is_3D_image = depth > 0;
    // Set image creation information.
    vk::ImageCreateInfo image_info = {};
    image_info.imageType = is_3D_image ? vk::ImageType::e3D : vk::ImageType::e2D;
    image_info.format = format;
    image_info.extent = vk::Extent3D(width, height, max(uint32_t(1), depth));
    image_info.mipLevels = 1;
    image_info.arrayLayers = 1;
    image_info.samples = vk::SampleCountFlagBits::e1;
    image_info.tiling = tiling;
    image_info.usage = usage;
    image_info.sharingMode = vk::SharingMode::eExclusive;
    image_info.initialLayout = initial_layout;

    VmaAllocationCreateInfo allocation_info = {};
    allocation_info.usage = VMA_MEMORY_USAGE_AUTO;

    uint32_t memoryTypeIndex = 0;
    allocation_info.memoryTypeBits = 0u << memoryTypeIndex;

    VmaAllocation allocation;
    vk::Image image;
    VkResult result = vmaCreateImage(
        vma_allocator,
        (VkImageCreateInfo*)&image_info,
        &allocation_info,
        (VkImage*)&image,
        &allocation,
        nullptr);

我试着改变allocation_info.usage，我尝试改变allocation_info.memoryTypeBits。在创建VMA结构时，我尝试将所有设备限制设置为0，但第一个堆除外。

我读了三遍：type.html

我不明白如何告诉VMA请从堆0中分配。

Answer 1

VMA的VmaAllocationCreateInfo结构有一个名为memoryTypeBits的成员。这允许您提供一组内存类型，VMA必须从中选择分配。因此，您可以从Vulkan获得一组内存类型，并且只指定使用堆0的内存类型。

尽管如此，这个问题发生的事实应该让你重新考虑VMA。堆2专门用于从CPU高效地将数据流到GPU。这很容易确定，因为使用它的所有内存类型都是主机可见的。

但是，除非图像使用线性拼接，否则不能直接写入图像的字节。因此，当其他非主机可见的内存类型可用时，VMA根本不需要使用主机可见内存类型(除非您的其他标志之一需要它)。如果图像不是线性平铺的，并且您没有告诉VMA确保内存是主机可见的，那么它的算法存在一个缺陷，应该让您重新考虑如何使用它。