On 09.12.24 15:28, Lorenzo Stoakes wrote:
On Mon, Dec 09, 2024 at 03:09:26PM +0100, David Hildenbrand wrote:
On 09.12.24 11:06, Lorenzo Stoakes wrote:
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.
And then we have mprotect.c being heavily used by uffd-wp and NUMA hinting,
which don't perform any VMA modification.
That's why I don't think the change proposed here is really the right step.
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.
And fork and such stuff. And if you look into huge_memory.c, we actually
moved all of the THP logic for mprotect()/madvise()/... in there.
Not sure if something similar should have been done for memory.c, or if the
THP stuff should actually also have gone into the respective files.
To me it sounds wrong to have VMA maintainers maintain a lot of the code in
these files code because these files somehow modify VMAs, sorry.
This isn't what I said, I said that de facto we (that is the MEMORY MAPPING
maintainers as well as VMA) were dealing with a great many issues around
page tables and page table manipulation which are rather inseparable from
one another.
I even went to the lengths of writing a detailed set of documentation on
locking behaviour in and around page table manipulation and solved
security-sensitive issues in relation to page table teardown over the 6.12
rc cycle.
To me, the idea that mprotect() and mlock(), operations that are explicitly
about manipulating VMAs (_and of course consqeuent page table
manipulation_), are somehow separate is really bizarre to me, but I respect
your opinion even if I disagree.
> > But unfortunately your arguments apply equally as well to mremap.c
(more
than half of which is dedicated to page table manipulation), so I will have
to drop the whole patch then.
If issues arise there in future, I guess others will have to deal with them
if we don't notice them (luckily Jann did and pinged this time, hopefully
will in future).
Again, the main point I have is that basic VMA handling (the now very
nice vma.c! ) that wouldn't even require page table modifications (the
very nice testing framework you added) is different to users of that
functionality.
And I agree that many VMA modification users imply page table
modifications and more.
--
Cheers,
David / dhildenb
To be clear, I made this change in the interests of the community and
contributing. It seems to me that within mm has far too little sharing of
the maintainership burden and I only wanted to help with that and make
explicit what I work on day-to-day.
And I appreciate that. But putting everything that touches VMAs under
VMA is wrong to me.
I am glad you at least don't object to my doing so with respect to at least
some parts of the VMA logic.
I really enjoy how well you separated the core VMA logic from everything
else.
--
Cheers,
David / dhildenb
