I just noticed if I do
time fstrim /<some ext4>; time fstrim /<some ext4> the 2nd call usually print
0 bytes trimmed and finished immediately. However if I do same thing on XFS, 2 of the calls are taking exactly same time and print exactly same amount of trimmed bytes. This makes me wonder does the trim really worked? If yes, is there any flag I can turn on to make the XFS not re-trim the already trimmed blocks?
I used all default settings to mount xfs.