Vulkan Memory Allocator usage in VulkanStagePool class

[adam-sawicki-a]

Hello, I'm the author of Vulkan Memory Allocator library. Thanks for using the library in your project.

I would like to suggest that in file VulkanStagePool.cpp, in function VulkanStagePool::acquireStage, memory usage should be VMA_MEMORY_USAGE_CPU_ONLY rather than VMA_MEMORY_USAGE_CPU_TO_GPU because that's the flag recommended for buffers that are used only as a source of transfer and not directly accessed by GPU while rendering.

By the way, I would also suggest to use version of the library from "development" branch, not from "master", as this release is quite old. You can find there functions to flush and invalidate memory (vmaFlushAllocation, vmaInvalidateAllocation), which you should do before/after mapping for memory types that are not coherent. This is important on mobile platforms, and I couldn't find any such calls (like vkFlushMappedMemoryRanges/vkInvalidateMappedMemoryRanges) in your current code.

[romainguy]

Thanks Adam! The Vulkan backend is still a work in progress, but this is very valuable information. And thanks for the library, it saved us a ton of time.

[prideout]

Ah, thanks for the note Adam, we'll definitely fix this stuff up and update the library!

Another issue is that we're not calling the defrag function anywhere...

[adam-sawicki-a]

There is no need to call defrag function. Currently defragmentation works only with HOST_VISIBLE (CPU) memory anyway. Allocation algorithm should do a good job at finding optimal place for new allocations.