It’s more about the characteristics of the workload than the size of the system. On a 1GB RAM system with fairly stable processes with chunks of RAM, the default 2MB hugepages can reduce TLB thrashing and improve performance; the TLB doesn’t begin to cover the mappings for 1GB of RAM. It’s generally just a tradeoff between CPU spent looking for memory to coalesce and TLB cache misses, and there are plenty of workloads on 1GB machines that can benefit considerably from THP. (Many recommendations to disable it come from early in its implementation; it has been substantially improved since.) The recommendation to disable THP for Discourse it is not because of the 1GB RAM size, but is specific to using redis with on-disk persistence which is something Discourse uses:
Unfortunately when a Linux kernel has transparent huge pages enabled, Redis incurs to a big latency penalty after the
forkcall is used in order to persist on disk. Huge pages are the cause of the following issue:
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