Tip submitted by my friend J.K when we were in need of a way to recover reserved cache space without booting.
In root:
PageCache only:
sync ; echo 1 > /proc/sys/vm/drop_caches
Dentries and inodes:
sync ; echo 2 > /proc/sys/vm/drop_caches
PageCache, Dentries and inodes:
(not recommanded in production as it forces a full cache rebuilt. you may still need it):
sync ; echo 3 > /proc/sys/vm/drop_cachesIn case you need to do it in a sudo:
echo 3 | sudo tee /proc/sys/vm/drop_caches