lkml.org 
[lkml]   [2023]   [Jul]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout
From
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

\
 
 \ /
  Last update: 2023-07-28 22:02    [W:0.403 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site