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This reverts commit 064512aa.

* remove workspace_handle in conv2d_cudnn
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* remove workspace_handle
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* fix bug
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* make test_conv2d_op SERIAL
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* save memory in conv_cudnn
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* enhance thread safety
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* enhance temporary allocator
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* Add excess fraction
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* follow comments
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* fix bug and code refine
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* fix memory size check
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* rename reuse_tmp_allocation_excess_fraction
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* Add Temporal Allocator

* add Temporay Allocator to DeviceContext
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* code refine
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* fix mean_iou
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* Add DeviceTemporaryAllocator
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* fix conv_op bug
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* small fix
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* code refine
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* log refine
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* fix unit test
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* move double check

* refine concat_and_split
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* add limit_of_temporary_allocation
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* fix name
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