Re: [RFC PATCH 05/12] fs/proc/task_mmu: refactor pagemap_pmd_range()

Jason Gunthorpe
2025-10-28T12:53:00Z

On Mon, Oct 27, 2025 at 04:38:05PM +0000, Lorenzo Stoakes wrote:
> On Mon, Oct 27, 2025 at 05:31:54PM +0100, David Hildenbrand wrote:
> > >
> > > I don't love the union.
> > >
> > > How would we determine what type it is, we'd have to have some
> > > generic_leaf_entry_t type or something to contain the swap type field and then
> > > cast and... is it worth it?
> > >
> > > Intent of non-present was to refer to not-swap swapentry. It's already a
> > > convention that exists, e.g. is_pmd_non_present_folio_entry().
> >
> > Just noting that this was a recent addition (still not upstream) that
> > essentially says "there is a folio here, but it's not in an ordinary present
> > page table entry.
> >
> > So we could change that to something better.
>
> Yeah but leaf_entry_t encapsulates BOTH swap and non-swap entries.
>
> So that's nice.
>
> What do you propose calling non-swap leaf entries? It starts spiralling down a
> bit there.

You don't even ask that question.

You have a leaf entry. It has a type.

What you are calling a "swap entry" is a "leaf entry of swap type".

The union helps encode in the type system what code is operating on
what type of the leaf entry.

It seems pretty simple.

> And it's really common to have logic asserting it's actually a swap entry
> vs. not etc.

leafent_is_swap(ent) - meaning is a "leaf entry of swap type".

> 1. we keep the non-present terminology as a better way of referring
> to non-swap entries.

I vastly prefer you leap ahead and start using leaf_entry
terminology. We don't need a temporary name we are going to throw
away.

Jason