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userfaultfd is an extremely intriguing hammer :)

The write protected mode[1], if it ever gets merged could have some interesting uses for GCs.

[1] https://lore.kernel.org/patchwork/cover/1033856/

I first learned about userfaultfd's utility to GC from https://medium.com/@MartinCracauer/generational-garbage-coll...

I could imagine it being interesting for VMs and DBs too. Imagine a VM whose memory "looks" like virtual memory but under the hood is transparently persisted between invocations.

That's kind of one of the main uses of the API so far by QEMU for live migration of VMs by streaming memory on demand over a network https://wiki.qemu.org/Features/PostCopyLiveMigration

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