EAGAIN during UFFD handling

[ValentaTomas]

Hey, when serving snapshots with hugepages via UFFD, I’m sometimes getting EAGAIN errors that are not resolved by retrying (for cca 200ms—4096 retries with minimal 50µs delay).

I’m not using balloon device, so I think the behavior described here and here should not apply, but my UFFD handler is still getting the continuous EAGAINs even though very randomly.

Any ideas or advice about what to try?

[Manciukic]

Duplicate of #5056