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… to allow loose packing to allow total fluxes that don't fit evenly into the requested number of sub-batches.
…mplex fragmentation.
…lux method which is rename to make_photon_subbatches.
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This is ready for review, though CI failed earlier on today during Conda setup: |
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Currently, the sub-batching in photon pooling is performed object-by-object. So, for example, if there are 100 objects in the batch, and 20 sub-batches, then the first five objects will go in the first sub-batch, the next five in the second, and so on. This means that if the objects vary a lot in brightness (and they do) then the flux per sub-batch will also vary a lot. In a typical run and setup provided by Jim, I found that most sub-batches contained a few thousand photons, and a handful contained several tens of millions. This leads to regular memory spikes when those sub-batches are processed in each new photon pool.
This PR smooths those memory spikes out by creating sub-batches with roughly equal fluxes. This is an implementation of the bin packing problem with fragmentation: our goal is to split the total flux in the pool across the sub-batches, and to achieve this we have to be able to fragment those extremely bright objects across however many sub-batches.
At the same time, each object fragmentation means another object lookup, and we had determined previously that with photon pooling these can mount up and become quite costly. For this reason, I'm allowing the flux in each sub-batch to vary slightly, letting objects to fill up over the limit to 105% of the expected per sub-batch flux if it prevents a fragmentation.
This is ready to go, but needs #511 to be merged in first and then this should be rebased onto it - so for now I'm leaving this as a draft.