Comment (by Roland Haas):

There is also the issue that during a regrid Carpet will genuinely use more memory, if I understand its code correctly then it can use “old grid” + “new grid” + “procbuf” where procbuf can be as much as the larger of “old grid” or “new grid”. At least operation normally happens in a group-by-group and level-by-level so that not two copies of the full state vector of all variables is required.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2194/memory-increase-during-regridding