linux-kernel - Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page mechanism

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Message-ID: <70d12456-1274-4876-a45f-a4c5fad87a61@lucifer.local>
Date: Sat, 26 Oct 2024 08:40:07 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
        "Paul E . McKenney" <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Muchun Song <muchun.song@...ux.dev>,
        Richard Henderson <richard.henderson@...aro.org>,
        Matt Turner <mattst88@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>, Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, Arnd Bergmann <arnd@...nel.org>,
        linux-alpha@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-arch@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>, Christian Brauner <brauner@...nel.org>,
        linux-kselftest@...r.kernel.org,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Jeff Xu <jeffxu@...omium.org>, Christoph Hellwig <hch@...radead.org>,
        linux-api@...r.kernel.org, John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v3 3/5] mm: madvise: implement lightweight guard page
 mechanism

On Fri, Oct 25, 2024 at 05:11:31PM -0700, Andrew Morton wrote:
> On Thu, 24 Oct 2024 08:25:46 +0100 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:
>
> > I actually do plan to extend this work to support shmem and file-backed
> > mappings in the future as a revision to this work.
>
> Useful, thanks.  I pasted this in.
>
> > >
> > > (generally, it would be nice to include the proposed manpage update at
> > > this time, so people can review it while the code change is fresh in
> > > their minds)
> >
> > It'd be nice to have the man pages live somewhere within the kernel so we
> > can do this as part of the patch change as things evolve during review, but
> > obviously moving things about like that is out of scope for this discussion
> > :)
>
> Yes, that would be good.  At present the linkage is so poor that things
> could get lost.

Things _have_ got lost. I don't see MADV_DONTNEED_LOCKED in the madvise()
man page for instance...

(I intend actually to send a patch for that alongside my changes.)

>
> I guess one thing we could do is to include the proposed manpage update
> within the changelogs.  That way it's stored somewhere and gets reviewed
> alongside the patches themselves.

Hm it won't be a diff but I do like the idea... let me come up with
something.

>
> > I do explicitly intend to send a manpage update once this series lands
> > however.
>
> That's late, IMO.  Sometimes reviewing manpage updates leads people to
> ask "hey.  what about X" or "hey, that's wrong".  Michael Kerrisk was
> good at finding such holes, back in the day.
>

Right, this is the problem with having the manpages in a separate repo, it
seems presumptious to _assume_ this will land in 6.13 though I hope it
does, but if I get a patch accepted in the manpages they may ship a version
that has information that is simply invalid...

Really would be nice to integrate it here :)

Michael Kerrisk is a hero, writes with a power of clarity I could only
dream of :) understandable that he may be rather tired of having to
maintain all this however...