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ZeRO 2 + Pipelining is broken. After hunting down the issue here (EleutherAI/gpt-neox#62), I've made a patch that seems to solve the issue but might create bad inefficiencies elsewhere.
Since this class turns
enable_backward_allreduce
off,self.overlapping_partition_gradients_reduce_epilogue()
defined in theDeepSpeedEngine
class never actually runs. I suspect this is because of efficiency problems;get_flat_partition
in stage2.py might do something expensive memorywise (a quick glance at the code certainly gives off that impression); someone will have to look into that later. But in the meantime, this fixes ZeRO2 + Pipelining enough to run a demo.