memory optimization for dynamic RNN #8041
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QiJune requested review from dzhwinter, reyoung, tonyyang-svail and wangkuiyi 
dzhwinter previously approved these changes Feb 1, 2018
| cur_scope.Rename(new_inside_name, inside_grad_name); | ||
| } | ||
| dev_ctx.Wait(); | ||
| const_cast<framework::Scope &>(scope).DeleteScope(&cur_scope); |
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Nice catch!
This fix will solve the headache OOM.
paddle/framework/scope.h Outdated
| /// Drop all kids scopes belonged to this scope. | ||
| void DropKids(); | ||
| | ||
| void EraseVars(std::vector<std::string>& var_names); |
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Since our every variable will be released after we destruct the scope, In my humble view, this interface should never be used.
| sum_op->Run(cur_scope, dev_place); | ||
| cur_scope.Rename(new_inside_name, inside_grad_name); | ||
| } | ||
| dev_ctx.Wait(); |
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what is the cost of adding this dev_ctx.Wait();?
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I have not make detailed test yet. But if we do not delete the step scope, we can not training a larger RNN model because of OutOfMemory.
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Have tested in machine translation demo.
In the first batch training, memory reduced from 5728446208 to 1115982080, saves 80.5% memory.
It seems that delete_var operator has no contribution for the result. I will remove it.