There are three options available to flush the cache of Linux memory. Use one of below as per your requirements.
Free pagecache, dentries and inodes in cache memory
echo 3 > /proc/sys/vm/drop_caches
Free dentries and inodes use following command
echo 2 > /proc/sys/vm/drop_caches
Free pagecache only use following command
echo 1 > /proc/sys/vm/drop_caches
Check Memory
watch -n 3 cat /proc/meminfo
watch -n 3 free -h
free -h