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
