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Manually compact GC before fork #2093

Merged
merged 1 commit into from Dec 18, 2019
Merged

Manually compact GC before fork #2093

merged 1 commit into from Dec 18, 2019

Commits on Dec 18, 2019

  1. Manually compact GC before fork 

    Rub 2.7.0 introduced `GC.compact` which allows manual compaction of Ruby slots. A good time to do this is before forking so that memory fragmentation can be reduced.

- https://www.ruby-lang.org/en/news/2019/12/17/ruby-2-7-0-rc1-released/
- https://www.youtube.com/watch?v=1F3gXYhQsAY

One issue with memory fragmentation when forking is that while a page in memory might have only one free slot, as that slot is written to after fork, the entire page is written so the benefit of CoW optimizations are greatly reduced. Manually compacting GC reduces the number of pages with empty slots.

This PR manually compacts memory right before Puma forks and after other `before_fork` hooks are called.
    @schneems
    schneems committed Dec 18, 2019
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