How much memory is available for Metal in iOS?

In my iOS project Metal is used extensively. Sometimes MTLDevice newTextureWithDescriptor fails to create a texture. Texture format is valid, it's a small RGBA 512x512 texture, everything is set up correctly.

When I print MTLDevice.currentAllocatedSize >> 20 it's always 1396 MB on iPhone XR ( A12 processor ).

I've used a lot this thread for max runtime RAM estimate: https://stackoverflow.com/a/15200855/2567725
So I believe for iPhone XR max allowed RAM is 1792 MB.

I guess the texture is not created because RAM has been exsausted.

So the guestions are:

1. Is it true that on A12 Metal's currentAllocatedSize correlates with CPU memory, and GPU memory is "shared" with the CPU one, so 1792 MB = GPU+CPU for iPhone XR ?

2. Is there any way to get the description of Metal error? (now it just returns nil in newTextureWithDescriptor).

3. Is it possible to know how Metal allocation strategy works, e.g. how small available RAM should be to MTLDevice newTextureWithDescriptor return nil ?

from How much memory is available for Metal in iOS?