1) n9 not n900
2) re: emmc supporting trim, i said that earlier:
3) defragging does not give the benefits that you claim. {TRIMing does} wear-leveling in the controller and optimizations in the filesystem make defragging less than helpful {at marking blocks as unused; performance of contiguous data is obviously the same as noncontiguous data on flash}. defragging moves blocks around, it does not mark blocks that are no longer used as discarded. defragging regularly is a TERRIBLE idea, but not nearly as bad intentionally erasing the data and rewriting it.

please, kids, DO NOT DEFRAG FLASH MEMORY, EVER.
dont do large erase/restores needlessly! never put off til tomorrow what you can put off until overmorrow!

if you have a device that has constantly changing data with a controller that supports TRIMing, run an operating system with a tool for TRIM like fstrim, and worry about performance, run fstrim once a week or so.

mostly, tho, stop worrying about perceived performance regressions, and actually take empirical measurements!