UpdateBuffer size limit #367

Hi, I am trying to update a big buffer to the GPU with code:

Diligent::BufferDesc desc;
desc.Name = "InstanceBuffer";
desc.Usage = Diligent::USAGE_DYNAMIC;
desc.BindFlags = Diligent::BIND_VERTEX_BUFFER;
desc.CPUAccessFlags = Diligent::CPU_ACCESS_WRITE;
desc.Size = this->capacity * sizeof(InstanceData);
pDevice->CreateBuffer(desc, nullptr, &this->instanceBuffer);
……
Diligent::MapHelper<uint8_t> mapped(pContext, instanceBuffer, Diligent::MAP_WRITE, Diligent::MAP_FLAG_DISCARD);
memcpy(mapped, instanceData.data(), instanceData.size() * sizeof(InstanceData));

Here’s the situation:
The data size I need to upload each frame is about 32 MB (1000 × 1000 × 2 × sizeof(float4x4)). When I run the code, the MapHelper() call fails. I'm using Diligent Engine 2.5.6, and my code is based on the samples (inherited from SampleBase).

The issue only appears when rendering 1000×1000 objects. With 100×100 objects, everything works fine, so the frame seems ok.

1. With Vulkan backend: the program crashes.
   2 With OpenGL backend: it rendered a mess (but does not crash immediately).
   I also tried increasing DynamicHeapSize to 64 MB in ModifyEngineInitInfo via EngineVkCI.DynamicHeapSize = 64 << 20. After that, it no longer crashes, but rendered a mess.

I’m wondering: Is there a size limitation for dynamic buffers (or the upload buffer) in Diligent? What is the best practice for uploading a large buffer (around 32 MB) to the GPU on a per‑frame basis?