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d=hostedemail.com; t=1762568951; a=rsa-sha256; cv=none; b=7U/gQrwaLmrpgFA441B91KXojG3buOZmOhw3WsySFyueoIdFJ4ksbXCwcGmS2U52taNsQg q8Z73/bfyBcV09NXvv65O5IrDRbgS8RibvTz8HXEB/s2VpCqBdlYBtjNxO/J/mf5ICruoW SpIdELJTymY6Fg/PzutQ26gxI2f9S2k= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=none; spf=pass (imf03.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none X-AuditID: a67dfc5b-c45ff70000001609-cc-690eaaf5facf Date: Sat, 8 Nov 2025 11:29:04 +0900 From: Byungchul Park To: Jakub Kicinski Cc: linux-mm@kvack.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel_team@skhynix.com, harry.yoo@oracle.com, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, saeedm@nvidia.com, leon@kernel.org, tariqt@nvidia.com, mbloch@nvidia.com, andrew+netdev@lunn.ch, edumazet@google.com, pabeni@redhat.com, akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, horms@kernel.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, ilias.apalodimas@linaro.org, willy@infradead.org, brauner@kernel.org, kas@kernel.org, yuzhao@google.com, usamaarif642@gmail.com, baolin.wang@linux.alibaba.com, almasrymina@google.com, toke@redhat.com, asml.silence@gmail.com, bpf@vger.kernel.org, linux-rdma@vger.kernel.org, sfr@canb.auug.org.au, dw@davidwei.uk, ap420073@gmail.com, dtatulea@nvidia.com Subject: Re: [RFC mm v5 1/2] page_pool: check nmdesc->pp to see its usage as page pool for net_iov not page-backed Message-ID: <20251108022904.GA1450@system.software.com> References: <20251103075108.26437-1-byungchul@sk.com> <20251103075108.26437-2-byungchul@sk.com> <20251106173320.2f8e683a@kernel.org> <20251107015902.GA3021@system.software.com> <20251106180810.6b06f71a@kernel.org> <20251107044708.GA54407@system.software.com> <20251107174129.62a3f39c@kernel.org> <20251108022458.GA65163@system.software.com> MIME-Version: 1.0 Content-Type: text/plain; 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Can we not move owner > > to _pp_mapping_pad ? Or reorder it with type, enum net_iov_type > > only has 2 values we can smoosh it with page_type easily. > > I'm still confused. I think you probably understand what this work is > for. (I've explained several times with related links.) Or am I ^ Please don't mind. It's not a blame. Byungchul > missing something from your questions? > > I've answered your question directly since you asked, but the point is > that, struct net_iov will no longer overlay on struct page. > > Instead, struct netmem_desc will be responsible for keeping the pp > fields while struct page will lay down the resonsibility, once the pp > fields will be removed from struct page like: > > (the current form is:) > > struct page { > memdesc_flags_t flags; > union { > ... > struct { > unsigned long pp_magic; > struct page_pool *pp; > unsigned long _pp_mapping_pad; > unsigned long dma_addr; > atomic_long_t pp_ref_count; > }; > ... > }; > unsigned int page_type; > ... > }; > > struct net_iov { > union { > struct netmem_desc desc; > struct > { > unsigned long _flags; > unsigned long pp_magic; > struct page_pool *pp; > unsigned long _pp_mapping_pad; > unsigned long dma_addr; > atomic_long_t pp_ref_count; > }; > }; > struct net_iov_area *owner; > enum net_iov_type type; > }; > > (the final form should be, just around the corner:) > > struct page { > memdesc_flags_t flags; > union { > ... > /* pp fields are gone. */ > ... > }; > unsigned int page_type; > ... > }; > > struct net_iov { > struct netmem_desc desc; > struct net_iov_area *owner; > enum net_iov_type type; > }; > > After that, struct page and struct net_iov(or struct netmem_desc) will > not share any fields with each other, probably they will be connected > e.i. through some ways between struct page and netmem_desc tho. > > Byungchul > > > > Yeah, you can tell 'why don't we add the field, page_type, to struct > > > net_iov (or struct netmem_desc)' so as to be like: > > > > > > struct net_iov { > > > union { > > > struct netmem_desc desc; > > > struct > > > { > > > unsigned long _flags; > > > unsigned long pp_magic; > > > struct page_pool *pp; > > > unsigned long _pp_mapping_pad; > > > unsigned long dma_addr; > > > atomic_long_t pp_ref_count; > > > + unsigned int page_type; // add this field newly > > > }; > > > }; > > > struct net_iov_area *owner; // the same offet of page_type > > > enum net_iov_type type; > > > }; > > > > > > I think we can make it anyway but it makes less sense to add page_type > > > to struct net_iov, only for PGTY_netpp. > > > > > > It'd be better to use netmem_desc->pp for that purpose, IMO.