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

[David Hildenbrand]

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!

--
Cheers,

David / dhildenb