Process (was Re: [PATCH mm-hotfixes-unstable v18 00/14] khugepaged: add mTHP) collapse support

[Lorenzo Stoakes <ljs@kernel.org>]

[trimmed cc list to avoid noise, apologies if I excluded anybody who is
interested in this!]

On Fri, May 22, 2026 at 11:13:42PM +0200, David Hildenbrand (Arm) wrote:
> On 5/22/26 18:11, Nico Pache wrote:
> > On Fri, May 22, 2026 at 9:13 AM Vlastimil Babka (SUSE)
> > <vbabka@kernel.org> wrote:
> >>
> >> On 5/22/26 17:07, Nico Pache wrote:
> >>>
> >>> Whoops I manually changed the coverletter subject to reflect that this
> >>> in on mm-hotfixes-unstable but never updated the others...
> >>
> >> But why? That branch is for hotfixes that would go to the current 7.1-rcX
> >> series. mm-unstable would be the correct one for this, AFAICT.
> >
> > Sorry this was a misunderstanding. The goal here was to base this off
> > the closest base commit behind where my v17 already lies in the tree.
>
> Ah, I guess this is a problem of "v17 is already in mm-unstable, so against what
> to base v18".
>
> Yeah, we touched on that problem in the LSF/MM process discussion ...

I may be misremembering but... :) [correct me if wrong]:

Wasn't the general conclusion that we maintain a stable branch (Linus's tree +
stuff that's been reviewed and is locked in for next release), and have people
base work against that?

This would be 'source of truth' and what we eventually send to Linus.

In that world, the maintainers perform conflict resolution, but with git rerere
we need only do this once.

We'd have mm-new which would contain everything for testing.

SO my question is - would we even need an mm-unstable in that world?

What role would it perform? Surely we'd want the stable branch going to
linux-next, so it's not that, it's not quite initial testing either as
mm-new would perform that duty.

It would potentially make life a bit easier for somebody doing a new series
to avoid merge conflicts, but that could then make life harder because
there'd be an implicit dependency of their series on what's-in-mm-unstable?

If everything's based on the stable branch, things are surely clearer?

Curious what people think here.

(I also wonder if we could have branches for versions of series so we could
do some kind of an easy diff between versions but maybe that'd create too
much noise :)

>
> --
> Cheers,
>
> David

Thanks, Lorenzo