What's copy-on-write (CoW) at the page level?
When the parent or child writes to a shared page, the OS page-fault handler traps the write, duplicates that single page, and lets the write proceed on the copy. All other pages remain shared.
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Copy-on-Write Snapshotsfork() shares parent memory, copying only written pages for non-blocking snapshots. Write-heavy loads can spike memory to 2x under load.
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