about compress table (no replies)

hi,all
i readed something about compress table from doc ,it says if the number of compress failure great than innodb_compression_failure_threshold_pct mysql will leave more free space within each new compressed page,

my question is:
1, how to calculate innodb_compression_failure_threshold_pct, the number of compress failure/ what?? = innodb_compression_failure_threshold_pct
2, how can mysql leave more free space to compressed page?
from doc context ,i guess mysql will split the old compress page to two new compress page
3, how can i monitor the times which the number of compress failure and the number of page split? so i can adjust the variable according the situation