Comment author: Camarade_Tux

I had forgotten about Bigarrays which have let me reduce memory usage (has been divided by three). Now, should int arrays take less memory or should the documentation be extended to warn about memory usage and point to bigarrays ?

Comment author: @damiendoligez

This is (more or less) done on purpose. Because of the incremental garbage collector, for every 10 bytes that are in use by your data, there are another 8 bytes allocated to hold the dead data that will be reclaimed by the current (or the next) GC cycle. This 80% overhead is the "space_overhead" parameter of the GC. By lowering this parameter, you can reduce memory consumption at the cost of more time spent in the GC. In your case, if you have a few very large arrays with a very long lifetime, you should be able to reduce the space overhead quite a lot without paying too much in terms of run time.

Unfortunately, I don't know of a simple way to do this automatically.