Today I realized that my Linux Contabo VPS has a built-in script in /etc/cron.hourly that drops the cache every hour. I found it when I checked dmesg; there are so many "drop_caches: 1" lines.
I guess the memory is not dedicated, but shared via KVM memory ballooning.
It seems Contabo tries so hard to reclaim physical memory from its customers by dropping page caches every hour. I feel like Contabo is somewhat notorious for aggressive overprovisioning.
I will delete the free script.
