Refactor Evented::Arena to allocate in blocks [fixup #14996]
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The main advantage is the ability to grow on demand and avoid a large single contiguous mmap of memory that needs to preallocates most of the memory. We also don't need to remember the maximum reached index anymore, which is replaced with a `#each_index` method (only needed to allow `fork`).
ysbaddaden
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Nov 19, 2024
straight-shoota
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Co-authored-by: Johannes Müller <[email protected]>
straight-shoota
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Nov 19, 2024
straight-shoota
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Evented::Arena to allocate in blocks [fixup #14996]
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Follow up to #14996
Replaces the static
mmapthat must accommodate for as many file descriptors as allowed by ulimit/rlimit. Despite being virtual memory, not really allocated in practice, this led to out-of-memory errors in some situations.The arena now dynamically allocates individual blocks as needed (no more virtual memory). For simplicity reasons it will only ever grow, and won't shrink (we may think of a solution for this later). The original safety guarantees still hold: once an entry has been allocated in the arena, its pointer won't change.
The event loop still limits the arena capacity to the hardware limit (ulimit: open files).
Side effect: the arena don't need to remember the maximum fd/index anymore; that was only needed for
fork; we can simply iterate the allocated blocks now.