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 DudHg5js 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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 Thu, Apr 24, 2025 at 10:45:36AM +0200, David Hildenbrand wrote: > > > Probably the right way of attaching such metadata to a VMA would be > > > remembering it alongside the VMA in a very simple way. > > > > > > For example, when we perform a reservation we would allocate a refcounted > > > object and assign it to the VMA (pointer, xarray, whatever). > > > > > > Duplicating the VMA would increase the refcount. Freeing a VMA would > > > decrease the refcount. > > > > > > Once the refcount goes to zero, we undo the reservation and free the object. > > > > > > We would not adjust a reservation on partial VMA unmap (split + unmap A or > > > B), but I strongly assume that would just be fine as long as we undo the > > > reservation once the refcount goes to 0. > > > > Yeah this is a really good idea actually, almost kinda what refcounts are > > for haha... > > > > The problem is we talk about this idly here, but neither of us wants to > > actually write PAT code I'd say, so this may go nowhere. But maybe one of > > us will get so frustrated that we do this anyway but still... > > > > Then again - actually, is this something you are planning to tackle? > > I hate this much with that much passion that I'll give it a try for a couple > of hours, as it might fix the other issues we are seeing. So far it looks > like it cleans up stuff *beautifully*. Even VM_PAT can go ... :) To quote a film, let the hate flow through you :P I mean I am very familiar with this - vma merge, anon_vma, etc. there's a pattern... ;) > > ... and I think we still have space in vm_area_struct without increasing it > beyond 192 bytes. Hm, so you're thinking of a general field in the VMA? I thought this would belong to the PAT object somehow? Though getting rid of VM_PAT would be fantastic... I wonder if a _general_ VMA ref count would be a bit much just for this case. But maybe I misunderstand your approach :) Happy to obviously look and if not like some crazy thing just for PAT (you can understand why I would not like this) will be supportive :>) > > -- > Cheers, > > David / dhildenb > Cheers, Lorenzo