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

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Message-ID: <aC9Dez8CftbNPcbg@kernel.org>
Date: Thu, 22 May 2025 18:32:11 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Johannes Weiner <hannes@...xchg.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	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 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().

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.

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

> > I guess let me work that up so we can see how that looks?
> 
> I think it's worth exploring!
> 

-- 
Sincerely yours,
Mike.