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

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Message-ID: <03f18fef-32a0-426a-beee-fdbe4c55446d@lucifer.local>
Date: Thu, 22 May 2025 14:49:09 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
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>,
        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 02:45:30PM +0200, David Hildenbrand wrote:
> On 21.05.25 19:32, 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.
>
> As stated elsewhere (e.g., THP cabal yesterday): mctrl() or sth like that
> might be better.
>
> ... or anything else that doesn't (ab)use the "advise" terminology in an
> interface that will not only consume advises.

Ack, as per my other reply, will work up some pseudocode/API exploration (not
yet code) and mail it round to participants here so we can explore this idea.

>
> > >
> > > 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.
>
> Same here. I am not 100% sure process_madvise() is really the right thing to
> extend, but I do enjoy the SET_DEFAULT_EXEC option. I am also not a big fan
> of prctl() ...

Yeah agreed on both actually! :)

>
> --
> Cheers,
>
> David / dhildenb
>