`echo 2 > /proc/sys/vm/drop_caches` decreases active pages

Before running echo 2 > /proc/sys/vm/drop_caches the active page count was:

Active(anon):   36185016 kB

after the flush, active page count became:

Active(anon):   26430472 kB

every other meminfo metrics stayed mostly the same and the system shows that 10GB of ram was freed. These 10GB are not attributed to any of the processes. What could explain such behavior? I am running on kernel 6.8. Update: This happens when **madvise(MADV_DONTNEED)** is used to decommit RSS. If I use *MADV_FREE* instead then surpringly I do not see **hidden** kernel memory and total used memory is tightly correlated with the RSS of the main process.