linux-kernel - Re: [PATCH 3/5] mm: export zap_page_range_single and list_lru

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Message-ID: <718079e8-dd1e-400c-9b81-4c833722c83a@lucifer.local>
Date: Thu, 5 Feb 2026 12:18:02 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        David Hildenbrand <david@...nel.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <lossin@...nel.org>,
        Andreas Hindborg <a.hindborg@...nel.org>,
        Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>,
        kernel-team@...roid.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-mm@...ck.org, rust-for-linux@...r.kernel.org
Subject: Re: [PATCH 3/5] mm: export zap_page_range_single and list_lru_add/del

On Thu, Feb 05, 2026 at 12:07:00PM +0000, Alice Ryhl wrote:
> On Thu, Feb 05, 2026 at 11:29:04AM +0000, Lorenzo Stoakes wrote:
> > We either need a wrapper that eliminates this parameter (but then we're adding a
> > wrapper to this behaviour that is literally for one driver that is _temporarily_
> > being modularised which is weak justifiction), or use of a function that invokes
> > it that is currently exported.
>
> I have not talked with distros about it, but quite a few of them enable
> Binder because one or two applications want to use Binder to emulate
> Android. I imagine that even if Android itself goes back to built-in,
> distros would want it as a module so that you don't have to load it for
> every user, rather than for the few users that want to use waydroid or
> similar.
>
> A few examples:
> https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/blob/5711a17344ec7cfd90443374a30d5cd3e9a9439e/config#L10993
> https://salsa.debian.org/kernel-team/linux/-/blob/debian/latest/debian/config/arm64/config?ref_type=heads#L106
> https://gitlab.com/cki-project/kernel-ark/-/blob/os-build/redhat/configs/fedora/generic/x86/CONFIG_ANDROID_BINDER_IPC?ref_type=heads

I mean you should update the cover letter to make this clear and drop the whole
reference to things being temporary, this is a lot more strident than the cover
letter is.

In any case, that has nothing to do with whether or not we export internal
implementation details to a module.

Something being in-tree compiled gets to use actually far too many internal
interfaces that really should not have been exposed, we've been far too leniant
about that, and that's something I want to address (mm has mm/*.h internal-only
headers, not sure how we'll deal with that with rust though).

Sadly even with in-tree, every interface you make available leads to driver
abuse. So something compiled in-tree using X, Y or Z interface doesn't mean that
it's correct or even wise, and modularising forces you to rethink that.

folio_mkclean() is a great example, we were about to be able to make that
mm-internal then 2 more filesystems started using it oops :)

>
> Alice

Cheers, Lorenzo