Messages in this thread | | | Date | Fri, 28 Jul 2023 22:00:53 +0200 | Subject | Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout | From | David Hildenbrand <> |
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On 28.07.23 21:50, Peter Xu wrote: > On Fri, Jul 28, 2023 at 09:40:54PM +0200, David Hildenbrand wrote: >> Hmm. So three alternatives I see: >> >> 1) Use FOLL_FORCE in follow_page() to unconditionally disable protnone >> checks. Alternatively, have an internal FOLL_NO_PROTNONE flag if we >> don't like that. >> >> 2) Revert the commit and reintroduce unconditional FOLL_NUMA without >> FOLL_FORCE. >> >> 3) Have a FOLL_NUMA that callers like KVM can pass. > > I'm afraid 3) means changing numa balancing to opt-in, probably no-go for > any non-kvm gup users as that could start to break there, even if making > smaps/follow_page happy again. > > I keep worrying 1) on FOLL_FORCE abuse. > > So I keep my vote on 2).
Linus had a point that we can nowadays always set FOLL_NUMA, even with FOLL_FORCE.
... so maybe we want to let GUP always set FOLL_NUMA (even with FOLL_FORCE) and follow_page() never set FOLL_NUMA.
That would at least decouple FOLL_NUMA from FOLL_FORCE.
-- Cheers,
David / dhildenb
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