Re: [RFC 1/1] mm/madvise: fail MADV_PAGEOUT on VM_DROPPABLE VMA

[Lance Yang]

On Mon, Jan 20, 2025 at 9:57 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 20.01.25 14:47, Lance Yang wrote:
> > Hi Barry, David and Lorenzo,
> >
> > Thanks a lot for taking time to review!
> >
> > On Mon, Jan 20, 2025 at 6:45 PM Lorenzo Stoakes
> > <lorenzo.stoakes@xxxxxxxxxx> wrote:
> >>
> >> Sorry but NACK again on this :(
> >>
> >> On Mon, Jan 20, 2025 at 09:30:38AM +0800, Lance Yang wrote:
> >>> MADV_PAGEOUT should fail on VMAs with the VM_DROPPABLE flag. While
> >>> MADV_PAGEOUT is intended to move anonymous pages to swap, VM_DROPPABLE
> >>> should not be swapped out.
> >>>
> >>> There is an issue where using MADV_PAGEOUT on a VMA with the VM_DROPPABLE
> >>> flag behaves like MADV_DONTNEED, causing the pages to be dropped. This
> >>> could break the semantics of MADV_PAGEOUT, IMO.
> >>>
> >>> So, let's add a check to detect the VM_DROPPABLE flag before doing
> >>> MADV_PAGEOUT and returns -EINVAL.
> >>
> >> No, let's not.
> >
> > I think I completely got it wrong. Learning so much from your patient responses!
>
> Maybe you can make the documentation (man pages?) clearer in that
> regard? Thanks!

Of course, I will give it a try ASAP ;)

Thanks for your suggestion!
Lance

>
> --
> Cheers,
>
> David / dhildenb
>