Solaris 11.4 and user_reserve_hint_pct

A long time ago, we wrote about the /etc/system-parameter user_reserve_hint_pct. It limits the size of the ZFS ARC cache by proxy by essentially limiting the amount of the memory the kernel uses (to simplify it).

By proxy, because the ARC is more or less the only large structure inside the kernel that can shrink and grow signficantly in a kernel in a short time.You set the amount of memory that you want to “reserve” for applications, and whats left is for the kernel. The nice thing about this parameter is the fact, that you can change it while the system is running. But the “by proxy” has an important implication.