Re: [RFC PATCH 3/6] mm: nommu: fix an issue on map request to /dev/zero

CC Jeff

On Thu, 13 Aug 2026 at 16:11, Lorenzo Stoakes (ARM) <[email protected]> wrote:
>
> +cc Christoph
>
> On Thu, Aug 13, 2026 at 11:02:18PM +0900, Greg Kroah-Hartman wrote:
> > On Thu, Aug 13, 2026 at 09:43:37PM +0900, Daniel Palmer wrote:
> > > Hi Greg,
> > >
> > > On Thu, 13 Aug 2026 at 21:26, Greg Kroah-Hartman
> > > <[email protected]> wrote:
> > >
> > > > Given the age of this issue, I don't think anyone uses no-mmu systems
> > > > anymore :(
> > >
> > > There are a few of us using it for hobby stuff[0][1] and there are
> > > apparently people using it for actual commercial stuff.
> > > There was a session about this at LPC 2025...
> >
> > This patch is fixing a very obvious issue that showed up in the 5.10
> > kernel, which was released in December 2020.
> >
> > So I think the fact that no one has reported it before now means that no
> > one is actually using it :)
>
> Maybe Christoph has a view on this?
>
> I brought this up a couple years ago and he claimed there are commerical
> products which use the latest long-term stable kernel (6.18 at the time of
> writing).
>
> See https://lore.kernel.org/linux-mm/[email protected]/
>
> Christoph - can you explain why none of these vendors encountered any of these
> bugs or breakages?
>
> If they are doing fixes that are downstream only, then that argues against
> upstream nommu.
>
> If they are not, in fact, using long term stable kernels, that argues against
> upstream nommu.
>
> The fact they seem to be assigning zero resource to upstream also argues against
> upstream nommu.
>
> nommu continues to be a ongoing burden for core mm that interferes with work on
> real architectures on a fairly regularly basis, which argues against upstream
> nommu.
>
> I'm curious to learn what the arguments _for_ upstream nommu are?
>
> >
> > thanks,
> >
> > greg k-h
>
> --
> Cheers, Lorenzo