…ers=True in DDP

We only need to keep track of this for traversing the autograd graph
when find_unused_parameters=True. Without that, we populate and keep this
mapping in memory, which occupies sizeof(pointer) * number of grad accumulators
of extra memory.

Differential Revision: [D24154407](https://our.internmc.facebook.com/intern/diff/D24154407/)

[ghstack-poisoned]

…sed_parameters=True in DDP"


We only need to keep track of this for traversing the autograd graph
when find_unused_parameters=True. Without that, we populate and keep this
mapping in memory, which occupies sizeof(pointer) * number of grad accumulators
of extra memory.

Also renames the variable to something more meaningful. 

Differential Revision: [D24154407](https://our.internmc.facebook.com/intern/diff/D24154407/)

[ghstack-poisoned]

…sed_parameters=True in DDP"


We only need to keep track of this for traversing the autograd graph
when find_unused_parameters=True. Without that, we populate and keep this
mapping in memory, which occupies sizeof(pointer) * number of grad accumulators
of extra memory.

Also renames the variable to something more meaningful. 

Differential Revision: [D24154407](https://our.internmc.facebook.com/intern/diff/D24154407/)

[ghstack-poisoned]

…sed_parameters=True in DDP"


We only need to keep track of this for traversing the autograd graph
when find_unused_parameters=True. Without that, we populate and keep this
mapping in memory, which occupies sizeof(pointer) * number of grad accumulators
of extra memory.

Also renames the variable to something more meaningful. 

Differential Revision: [D24154407](https://our.internmc.facebook.com/intern/diff/D24154407/)

[ghstack-poisoned]

…sed_parameters=True in DDP"


We only need to keep track of this for traversing the autograd graph
when find_unused_parameters=True. Without that, we populate and keep this
mapping in memory, which occupies sizeof(pointer) * number of grad accumulators
of extra memory.

Also renames the variable to something more meaningful. 

Differential Revision: [D24154407](https://our.internmc.facebook.com/intern/diff/D24154407/)

[ghstack-poisoned]