linux-kernel - Re: [RFC PATCH 0/5] add process_madvise() flags to modify behaviour

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Message-ID: <ad20b26a-be45-454c-9f5d-4c488d108734@lucifer.local>
Date: Thu, 22 May 2025 16:47:07 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        David Hildenbrand <david@...hat.com>, Vlastimil Babka <vbabka@...e.cz>,
        Jann Horn <jannh@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <brauner@...nel.org>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        SeongJae Park <sj@...nel.org>, Usama Arif <usamaarif642@...il.com>
Subject: Re: [RFC PATCH 0/5] add process_madvise() flags to modify behaviour

On Thu, May 22, 2025 at 06:32:11PM +0300, Mike Rapoport wrote:
> On Wed, May 21, 2025 at 01:32:00PM -0400, Johannes Weiner wrote:
> > On Wed, May 21, 2025 at 05:21:19AM +0100, Lorenzo Stoakes wrote:
> > > So, something Liam mentioned off-list was the beautifully named
> > > 'mmadvise()'. Idea being that we have a system call _explicitly for_
> > > mm-wide modifications.
> > >
> > > With Barry's series doing a prctl() for something similar, and a whole host
> > > of mm->flags existing for modifying behaviour, it would seem a natural fit.
> >
> > That's an interesting idea.
> >
> > So we'd have THP policies and Barry's FADE_ON_DEATH to start; and it
> > might also be a good fit for the coredump stuff and ksm if we wanted
> > to incorporate them into that (although it would duplicate the
> > existing proc/prctl knobs). The other MMF_s are internal AFAICS.
> >
> > I think my main concern would be making something very generic and
> > versatile without having sufficiently broad/popular usecases for it.
> >
> > But no strong feelings either way. Like I said, I don't have a strong
> > dislike for prctl(), but this idea would obviously be cleaner if we
> > think there is enough of a demand for a new syscall.
>
> To me it seems like having a "global mm control" system call makes much
> more sense that adding more arms to prctl or overloading process_madvise().

Agreed yeah.

>
> With a dedicated syscall it's much clearer that the operation targets an mm
> and it works for the entire mm.
> And two usescase seem enough to me to justify a new syscall.

Yes I think so!

>
> And it's easier to reason about a dedicated syscall designed for a certain
> operation that for multiplexed ioctl() style controls.

Yes!

>
> > > I guess let me work that up so we can see how that looks?
> >
> > I think it's worth exploring!
> >
>
> --
> Sincerely yours,
> Mike.

Thanks, I will distribute a proposed mctl() prototype API to people here (+ cc
you + linux-api also) so we can use that as a basis to assess this approach.

Thanks!