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 HTFJtQtP 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 25, 2025 at 06:26:00AM -0400, Liam R. Howlett wrote: > * Lorenzo Stoakes [250425 06:09]: > > On Thu, Apr 24, 2025 at 06:22:30PM -0700, Suren Baghdasaryan wrote: > > > On Thu, Apr 24, 2025 at 2:22 PM David Hildenbrand wrote: > > > > > > > > On 24.04.25 23:15, Lorenzo Stoakes wrote: > > > > > Right now these are performed in kernel/fork.c which is odd and a violation > > > > > of separation of concerns, as well as preventing us from integrating this > > > > > and related logic into userland VMA testing going forward, and perhaps more > > > > > importantly - enabling us to, in a subsequent commit, make VMA > > > > > allocation/freeing a purely internal mm operation. > > > > > > > > > > There is a fly in the ointment - nommu - mmap.c is not compiled if > > > > > CONFIG_MMU is not set, and there is no sensible place to put these outside > > > > > of that, so we are put in the position of having to duplication some logic > > > > > > s/to duplication/to duplicate > > > > Ack will fix! > > > > > > > > > > here. > > > > > > > > > > This isn't ideal, but since nommu is a niche use-case, already duplicates a > > > > > great deal of mmu logic by its nature and we can eliminate code that is not > > > > > applicable to nommu, it seems a worthwhile trade-off. > > > > > > > > > > The intent is to move all this logic to vma.c in a subsequent commit, > > > > > rendering VMA allocation, freeing and duplication mm-internal-only and > > > > > userland testable. > > > > > > > > I'm pretty sure you tried it, but what's the big blocker to have patch > > > > #3 first, so we can avoid the temporary move of the code to mmap.c ? > > > > > > Completely agree with David. > > > > Ack! Yes this was a little bit of a silly one :P > > > > > I peeked into 4/4 and it seems you want to keep vma.c completely > > > CONFIG_MMU-centric. I know we treat NOMMU as an unwanted child but > > > IMHO it would be much cleaner to move these functions into vma.c from > > > the beginning and have an #ifdef CONFIG_MMU there like this: > > > > > > mm/vma.c > > > > This isn't really workable, as the _entire file_ basically contains > > CONFIG_MMU-specific stuff. so it'd be one huge #ifdef CONFIG_MMU block with > > one small #else block. It'd also be asking for bugs and issues in nommu. > > > > I think doing it this way fits the patterns we have established for > > nommu/mmap separation, and I would say nommu is enough of a niche edge case > > for us to really not want to have to go to great lengths to find ways of > > sharing code. > > > > I am quite concerned about us having to consider it and deal with issues > > around it so often, so want to try to avoid that as much as we can, > > ideally. > > I think you're asking for more issues the way you have it now. It could > be a very long time until someone sees that nommu isn't working, > probably an entire stable kernel cycle. Basically the longest time it > can go before being deemed unnecessary to fix. > > It could also be worse, it could end up like the arch code with bugs > over a decade old not being noticed because it was forked off into > another file. > > Could we create another file for the small section of common code and > achieve your goals? That'd completely defeat the purpose of isolating core functions to vma.c. Again, I don't believe that bending over backwards to support this niche use is appropriate. And if you're making a change to vm_area_alloc(), vm_area_free(), vm_area_init_from(), vm_area_dup() it'd seem like an oversight not to check nommu right? There's already a large amount of duplicated logic there specific to nommu for which precisely the same could be said, including entirely parallel brk(), mmap() implementations. So this isn't a change in how we handle nommu. > > Thanks, > Liam > >