在proxmox環境要新建vm，明明系統顯示記憶體仍有50%以上，但是在啟動vm時，卻失敗
if you're facing an issue of starting VM with this kind of error message below, it might be the reason that system kept too much caches of VMs,
錯誤訊息為：
ioctl(KVM_CREATE_VM) failed: 12 Cannot allocate memory
kvm: failed to initialize KVM: Cannot allocate memory
kvm: failed to initialize KVM: Cannot allocate memory
這時需要用一個指令將cache刪除掉
you can try to clean caches by using command as following, then use free command to check
free && sync && echo 3 > /proc/sys/vm/drop_caches && free
先檢視目前記憶體狀態，再drop_caches，最後再一次檢視記憶體是否已經釋出
虛擬環境還是很吃記憶體的，我看還是定期清一下cache比較好，決定加入排程去處理
maybe it is better to add this job into crontab and execute it regularly
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