Is 192GB RAM useless for AI build?

I built an AI PC using 2x 4090 GPUs and 7950X CPU. I also utilized an Asus ProArt X670E mobo and a 192GB DDR5 Corsair RAM kit(they are working @ 4800Mhz/s). It seems everything works fine and I haven't had any unstability issues so far. But when I check RAM usage during the inference of Stable Diffusion models, it only used 10%(around 18GB) of RAM(With only one GPU. I couldn't figure it out how to enable dual GPU usage).

I …

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