On Wed, Apr 09, 2025 at 01:28:37PM -0300, Jason Gunthorpe wrote: > On Wed, Apr 09, 2025 at 07:19:30PM +0300, Mike Rapoport wrote: > > But we have memdesc today, it's struct page. > > No, I don't think it is. struct page seems to be turning into > something legacy that indicates the code has not been converted to the > new stuff yet.
No, struct page will be with us for a while. Possibly forever. I have started reluctantly talking about a future in which there aren't struct pages, but it's really premature at this point. That's a 2030 kind of future. For 2025-2029, we will still have alloc_page(s)(). It's just that the size of struct page will be gradually shrinking over that time. > > And when the data structure that memdesc points to will be allocated > > separately folios won't make sense for order-0 allocations. > > At that point the lowest level allocator function will be allocating > the memdesc along with the struct page. Then folio will become > restricted to only actual folio memdescs and alot of the type punning > should go away. We are not there yet. We'll have a few allocator functions. There'll be a slab_alloc(), folio_alloc(), pt_alloc() and so on. I sketched out how these might work last year: https://kernelnewbies.org/MatthewWilcox/FolioAlloc > > > The lowest allocator primitive returns folios, which can represent any > > > order, and the caller casts to their own memdesc. > > > > The lowest allocation primitive returns pages. > > Yes, but as I understand things, we should not be calling that > interface in new code because we are trying to make 'struct page' go > away. > > Instead you should use the folio interfaces and cast to your own > memdesc, or use an allocator interface that returns void * (ie slab) > and never touch the struct page area. > > AFAICT, and I just wrote one of these.. Casting is the best you can do today because I haven't provided a better interface yet. > > And I don't think folio will be a lowest primitive buddy returns anytime > > soon if ever. > > Maybe not internally, but driver facing, I think it should be true. > > Like I just completely purged all struct page from the iommu code: > > https://lore.kernel.org/linux-iommu/0-v4-c8663abbb606+3f7-iommu_pages_...@nvidia.com/ > > I don't want some weird KHO interface that doesn't align with using > __folio_alloc_node() and folio_put() as the lowest level allocator > interface. I think it's fine to say "the KHO interface doesn't support bare pages; you must have a memdesc". But I'm not sure that's the right approach.
