Re-using identical COW entries ?

Hi.

Thinking about hashing and checksumming, I was wondering ...

Does BTRFS re-use identical COW entries ?
-Eg. if I'm compiling the same sources over and over, producing the same binaries over and over ...
Then the binaries would be deleted, then written again, deleted, ... repeat.

If deletion of unused entries would be just a bit that's set/cleared (which it's probably not, for safety), then 
a COW entry could be re-used quickly (making writes faster).

It would of course require that the COW entry is not modified since last time (but if it was, it would have a different hash/checksum anyway).

Reason for thinking this way, is because I just copied 1.9 TB backup onto a disk-image which is on a BTRFS volume; the disk image uses 1.7TB space so far (and I'm incrementally updating that backup) and I know I have several identical files. Using a disk-image, because seen from Linux, it's a non-native file format.


Love
Jens