SLAB CACHE optimize.

More info here: https://cloudlinux.zendesk.com/hc/en-us/articles/115004738025-What-to-do-if-Slab-cache-grows-and-overall-server-performance-is-bad

Check slab:
<code bash>
cat /proc/meminfo | egrep "MemTotal|Cached|Slab|SReclaimable|Buffers"
</code>

Paste to /etc/sysctl.conf
<code>
vm.vfs_cache_min_ratio=0
vm.vfs_cache_pressure=1000
</code>

DROP caches:
<code bash>
echo 2 > /proc/sys/vm/drop_caches
</code>