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0 pointsadsharma9d ago0 comments

Some more historical context. It wasn't a random optimization idea that I thought about in the shower and implemented the next day. Previous work on company wide profiling, where my contribution was low level perf_events plumbing:

https://research.google/pubs/google-wide-profiling-a-continu... https://engineering.fb.com/2025/01/21/production-engineering...

The profiling clearly showed kernel functions doing memzero at the top of the profiles which motivated the change. The performance impact (A/B testing and measuring the throughput) also showed a benefit at the point the change was committed.

This was when "facebook" was a ~1GB ELF binary. https://en.wikipedia.org/wiki/HipHop_for_PHP

The change stopped being impactful sometime after 2013, when a JIT replaced the transpiler. I'm guessing likely before 2016 when continuous deployment came into play. But that was continuously deploying PHP code, not HHVM itself.

By the time the patches were reevaluated I was working on a Graph Database, which sounded a lot more interesting than going back to my old job function and defending a patch that may or may not be relevant.

I'm still working on one. Guilty as charged of carrying ideas in my head for 10+ years and acting on them later. Link in my profile.

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genxy8d ago

This kind of thing always struck me as something that the MMU and the memory controller could team up on. When you give back memory, you could not refresh it for some cycles. Or you could DMA the same page of zeros over all of it, so the CPU isn't involved in menial labor.

adsharmaOP8d ago

This is an old debate that goes back 25+ years. One of the differences in how Linux and FreeBSD handle the issue.

Linux developers believe that involving the CPU warms the caches and is a good thing.

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