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If I recall this was about a very specific case where migration does a number of invalidations and some of the earlier ones are known to be redundant in this specific case. Redundant means it can be ignored without causing an inconsistency. Alistair would know, but I assumed this works OK because the above invalidation doesn't actually go on to free any pages but keeps them around until a later invalidation? This is nothing like what your case is talking about. Jason