revlog: increase I/O bound to 4x the amount of data consumed This doesn't affect normal clones since they'd be bound by the CPU bound below anyway -- it does, however, improve generaldelta clones significantly. This also results in better deltaing for generaldelta clones -- in generaldelta clones, we calculate deltas with respect to the closest base if it has a higher revision number than either parent. If the base is on a significantly different branch, this can result in pointlessly massive deltas. This reduces the number of bases and hence the number of bad deltas. Empirically, for a highly branchy repository, this resulted in an improvement of around 15% to manifest size.