Let's see: unstable/unusable server or correctly uses swap where required. hmmm. 
My file is like this, running like a charm:
24789 amavis 39 19 398716 261180 2968 R 12.5 25.7 0:07.05 clamd
My server:
CPU Details: 2 Core (2600 MHz)
RAM: 1Gb SWAP: 512Mb
Distro Name: CentOS Linux release 7.8.2003 (Core)
Kernel Version: 3.10.0-1127.19.1.el7.x86_64
[Unit]
Description = clamd scanner (%i) daemon
Documentation=man:clamd(8) man:clamd.conf(5) https://www.clamav.net/documents/
After = syslog.target nss-lookup.target network.target
[Service]
Type = simple
ExecStart = /usr/sbin/clamd -c /etc/clamd.d/amavisd.conf --foreground=yes
# Reload the database
ExecReload=/bin/kill -USR2 $MAINPID
Restart = on-failure
TimeoutStartSec=420
IOSchedulingPriority = 7
CPUSchedulingPolicy = 5
MemoryLimit = 256M
CPUQuota = 13%
Nice = 19
[Install]
WantedBy = multi-user.target