On Mon, 30 Jun 2025 08:34:48 +0900 Harry Yoo wrote: > > Ugh, you keep explaining the mechanics to me. Our goal here is not > > just to move fields around and make it still compile :/ > > > > Let me ask you this way: you said "netmem_desc" will be allocated > > thru slab "shortly". How will calling the equivalent of page_address() > > on netmem_desc work at that stage? Feel free to refer me to the existing > > docs if its covered.. > > https://kernelnewbies.org/MatthewWilcox/Memdescs/Path > https://kernelnewbies.org/MatthewWilcox/Memdescs > > May not be the exact document you're looking for, > but with this article I can imagine: > > - The ultimate goal is to shrink struct page to eventually from 64 bytes > to 8 bytes, by allocating only the minimum required metadata per 4k page > statically and moving the rest of metadata to dynamically-allocated > descriptors (netmem_desc, anon, file, ptdesc, zpdesc, etc.) using slab > at page allocation time. > > - We can't achieve that goal just yet, because several subsystems > still use struct page fields for their own purposes. > > To achieve that, each of these subsystems needs to define > its own descriptor, which, for now, overlays struct page, and should be > converted to use the new descriptor. > > Eventually, these descriptors will be allocated using slab. > > - For CPU-readable buffers, page->memdesc will point to a netmem_desc, > with a lower bit set indicating that it's a netmem_desc rather than > other type. Networking code will need to cast it to (netmem_desc *) > and dereference it to access networking specific fields. > > - The struct page array (vmemmap) will still be statically allocated > at boot time (or during memory hotplug time). > So no change in how page_address() works. > > net_iovs will continue to be not associated with struct pages, > as the buffers don't have corresponding struct pages. > net_iovs are already allocated using slab. Thanks a lot, this clarifies things for me. Unfortunately, I still think that it's hard to judge patches 1 and 7 in context limited to this series, so let's proceed to reposting just the "middle 5" patches.
