Re: [PATCH] MAINTAINERS: group all VMA-related files into the VMA section

[Lorenzo Stoakes]

On Mon, Dec 09, 2024 at 10:16:21AM +0100, David Hildenbrand wrote:
> On 06.12.24 20:16, Lorenzo Stoakes wrote:
> > There are a number of means of interacting with VMA operations within mm,
> > and we have on occasion not been made aware of impactful changes due to
> > these sitting in different files, most recently in [0].
> >
> > Correct this by bringing all VMA operations under the same section in
> > MAINTAINERS. Additionally take the opportunity to combine MEMORY MAPPING
> > with VMA as there needn't be two entries as they amount to the same thing.
> >
> > [0]:https://lore.kernel.org/linux-mm/CAG48ez0siYGB8GP5+Szgj2ovBZAkL6Zi4n6GUAjzzjFV9LTkRQ@xxxxxxxxxxxxxx/
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > ---
> >   MAINTAINERS | 19 +++++++------------
> >   1 file changed, 7 insertions(+), 12 deletions(-)
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 1e930c7a58b1..95db20c26f5f 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -15060,18 +15060,6 @@ F:	tools/mm/
> >   F:	tools/testing/selftests/mm/
> >   N:	include/linux/page[-_]*
> >
> > -MEMORY MAPPING
> > -M:	Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > -M:	Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> > -M:	Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > -R:	Vlastimil Babka <vbabka@xxxxxxx>
> > -R:	Jann Horn <jannh@xxxxxxxxxx>
> > -L:	linux-mm@xxxxxxxxx
> > -S:	Maintained
> > -W:	http://www.linux-mm.org
> > -T:	git git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> > -F:	mm/mmap.c
> > -
> >   MEMORY TECHNOLOGY DEVICES (MTD)
> >   M:	Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> >   M:	Richard Weinberger <richard@xxxxxx>
> > @@ -25028,6 +25016,13 @@ L:	linux-mm@xxxxxxxxx
> >   S:	Maintained
> >   W:	https://www.linux-mm.org
> >   T:	git git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
> > +F:	mm/madvise.c
> > +F:	mm/mlock.c
> > +F:	mm/mmap.c
> > +F:	mm/mprotect.c
> > +F:	mm/mremap.c
> > +F:	mm/mseal.c
> > +F:	mm/msync.c
>
> Not sure about mprotect.c, mlock.c and madvise.c, though. I'd claim that the
> real "magic" they perform is in page table handling and not primarily VMA
> handling (yes, both do VMA changes, but they are the "easy" part ;) ).

And large parts of the VMA logic interface with page tables, see - the entire
6.12 cycle - around recent changes in mmap() MAP_FIXED - which... the VMA
maintainers fixed :)

And then there were the issues around VMA and mm locking relating to page
table work which... oh right yeah we had to fix again... :>)

I mean you can make this argument about probably all of these files (mremap
has -tons- of page table-specific stuff), and then we get back to not being
notified about key changes that interface with memory mapping/VMA which we
end up having to deal with anyway.

A lot of the reason we have 'magic' in these files anyway is because we
don't have a decent generic page table handler. Not sure I'd actually use
the word 'magic' for that though.

I am planning to make significant changes to mprotect/mlock soon, which
have some terribly duplicated horrible handling logic, and both are key
considerations in VMA logic as a whole.

Anyway, as far as I'm concerned page table manipulation after the point of
faulting is completely within the purvue of VMA manipulation and a side
product of it.

However, can concede mm/madvise.c if you feel strongly about that as that's
a bit blurry, but of course contains a whole bunch of VMA and... page table
manipulation :) I mean it still to me seems very pertinent.

>
> They have much more in common with memory.c, which I wouldn't want to see in
> here either. Hm.

No, memory.c is really dedicated to fault handling. This is really
different from manipulating page tables in specific cases in my opinion.

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

In case you are concerned about how much code this actually spans, it's
~6ksloc out of ~127ksloc, with roughly half of that in mm/vma.c...