I tested again, i can only use 3 res blocks, if more ,it reports an error with exactly same number and words.
RuntimeError: CUDA out of memory. Tried to allocate 256.00 MiB (GPU 0; 10.92 GiB total capacity; 9.63 GiB already allocated; 223.50 MiB free; 458.66 MiB cached)

no matter 4,5,6,7 or 8 blocks i use in forward pass, it report this error, and the numbers are exactly same