For workload using forking and CoW sharing like Redis or CRuby it negates the entire benefit of CoW since flipping a single bit copies the entire huge page.
That's what used to happen but since kernel 5.8, anonymous shared pages that are dirtied by child processes are instead divided into normal pages, in the same way they would be if they were named (file-backed) mappings.
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THP is a net loss for many workloads, including PG https://www.percona.com/blog/2019/03/06/settling-the-myth-of...
For workload using forking and CoW sharing like Redis or CRuby it negates the entire benefit of CoW since flipping a single bit copies the entire huge page.
That's what used to happen but since kernel 5.8, anonymous shared pages that are dirtied by child processes are instead divided into normal pages, in the same way they would be if they were named (file-backed) mappings.