linux-kernel - Re: [RFC PATCH 00/12] remove is_swap

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Message-ID: <4fd565b5-1540-40bc-9cbb-29724f93a4d2@lucifer.local>
Date: Wed, 29 Oct 2025 19:09:59 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
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Subject: Re: [RFC PATCH 00/12] remove is_swap_[pte, pmd]() + non-swap
 confusion

On Wed, Oct 29, 2025 at 11:10:48AM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 28, 2025 at 06:20:54PM +0000, Lorenzo Stoakes wrote:
> > > > And use the new type right away.
> > >
> > > Then the followup series is cleaning away swap_entry_t as a name.
> >
> > OK so you're good with the typedef? This would be quite nice actually as we
> > could then use leaf_entry_t in all the core leafent_xxx() logic ahead of
> > time and reduce confusion _there_ and effectively document that swp_entry_t
> > is just badly named.
>
> Yeah, I think so, a commit message explaining it is temporary and a
> future series will mechanically rename it away and this is
> preparation.
>
> > I mean I'm not so sure that's all that useful, you often want to skip over
> > things that are 'none' entries without doing this conversion.
>
> Maybe go directly from a pte to the leaf entry type for this check?
>
> #define __swp_type(x) ((x).val >> (64 - SWP_TYPE_BITS))
>
> That's basically free on most arches..

That's nice, I guess we could throw in a pte_present() check there and just grab
the type out direct like that

>
> > We could use the concept of 'none is an empty leaf_entry_t' more thoroughly
> > internally in functions though.
> >
> > I will see what I can do.
>
> Sure, maybe something works out
>
> Though if we want to keep them seperate then maybe pte_is_leafent() is
> the right name for pte_none(). Reads so much better like this:
>
> if (pte_is_leafent(pte)) {

Ah so this would amount to !pte_is_present()

>     leafent_t leaf = leafent_from_pte(pte)
>
>      if (leafent_is_swap(leaf)) {..}

And yeah... that is nice you know... :)

> }

>
> > > Then this:
> > >
> > >   pmd_is_present_or_leafent(pmd)
> >
> > A PMD can be present and contain an entry pointing at a PTE table so I'm
> > not sure that helps... naming is hard :)
>
> pmd_is_leaf_or_leafent()
>
> In the PTE API we are calling present entries that are address, not
> tables, leafs.

Hmm I think pmd_is_present_or_leafent() is clearer actually on second
thoughts :)

Still feel a desire to shove a 'huge' in there though but then it's getting
wordy... :)

Let me play around...

>
> Jason

Cheers, Lorenzo