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imf19.hostedemail.com; dkim=none; spf=pass (imf19.hostedemail.com: domain of byungchul@sk.com designates 166.125.252.92 as permitted sender) smtp.mailfrom=byungchul@sk.com; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1748222149; a=rsa-sha256; cv=none; b=yrf56y9vssENj0OhStWudwE8vxd/kEFkRjdYsMLOHqzmnoyEcEVI7bBPH9N42vKRXXaJzy bAraJSHTD/8AwdrnKN4k6l16jJYv+giG3wM0nCfeB2Nth0jopOeXDwDKf98t9lQpIhgbR8 X9h6HDsNtseE8WzstNuEizo0iv+9yDo= X-AuditID: a67dfc5b-681ff7000002311f-0f-6833c0c0b097 Date: Mon, 26 May 2025 10:15:39 +0900 From: Byungchul Park To: Mina Almasry Cc: willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, kuba@kernel.org, ilias.apalodimas@linaro.org, harry.yoo@oracle.com, hawk@kernel.org, akpm@linux-foundation.org, davem@davemloft.net, john.fastabend@gmail.com, andrew+netdev@lunn.ch, asml.silence@gmail.com, toke@redhat.com, tariqt@nvidia.com, edumazet@google.com, pabeni@redhat.com, saeedm@nvidia.com, leon@kernel.org, ast@kernel.org, daniel@iogearbox.net, 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, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com Subject: Re: [PATCH 01/18] netmem: introduce struct netmem_desc struct_group_tagged()'ed on struct net_iov Message-ID: <20250526011539.GB74632@system.software.com> References: <20250523032609.16334-1-byungchul@sk.com> <20250523032609.16334-2-byungchul@sk.com> MIME-Version: 1.0 Content-Type: text/plain; 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> > }; > > struct { /* page_pool used by netstack */ > > + unsigned long _pp_mapping_pad; > > /** > > * @pp_magic: magic value to avoid recycling non > > * page_pool allocated pages. > > */ > > unsigned long pp_magic; > > struct page_pool *pp; > > - unsigned long _pp_mapping_pad; > > Like Toke says, moving this to the beginning of this struct is not > allowed. The first 3 bits of pp_magic are overlaid with page->lru so > the pp makes sure not to use them. _pp_mapping_pad is overlaid with > page->mapping, so the pp makes sure not to use it. AFAICT, this moving > of _pp_mapping_pad is not necessary for this patch. I think just drop > it. Sure, I will. Thanks. > > unsigned long dma_addr; > > atomic_long_t pp_ref_count; > > }; > > diff --git a/include/net/netmem.h b/include/net/netmem.h > > index 386164fb9c18..08e9d76cdf14 100644 > > --- a/include/net/netmem.h > > +++ b/include/net/netmem.h > > @@ -31,12 +31,41 @@ enum net_iov_type { > > }; > > > > struct net_iov { > > - enum net_iov_type type; > > - unsigned long pp_magic; > > - struct page_pool *pp; > > - struct net_iov_area *owner; > > - unsigned long dma_addr; > > - atomic_long_t pp_ref_count; > > + /* > > + * XXX: Now that struct netmem_desc overlays on struct page, > > + * struct_group_tagged() should cover all of them. However, > > + * a separate struct netmem_desc should be declared and embedded, > > + * once struct netmem_desc is no longer overlayed but it has its > > + * own instance from slab. The final form should be: > > + * > > + * struct netmem_desc { > > + * unsigned long pp_magic; > > + * struct page_pool *pp; > > + * unsigned long dma_addr; > > + * atomic_long_t pp_ref_count; > > + * }; > > + * > > + * struct net_iov { > > + * enum net_iov_type type; > > + * struct net_iov_area *owner; > > + * struct netmem_desc; > > + * }; > > + */ > > I'm unclear on why moving to this format is a TODO for the future. Why > isn't this state in the comment the state in the code? I think I gave > the same code snippet on the RFC, but here again: > > struct netmem_desc { > /** > * @pp_magic: magic value to avoid recycling non > * page_pool allocated pages. > */ > unsigned long pp_magic; > struct page_pool *pp; > unsigned long _pp_mapping_pad; > unsigned long dma_addr; > atomic_long_t pp_ref_count; > }; > > (Roughly): > > struct page { > ... > struct { /* page_pool used by netstack */ > struct netmem_desc; This is unnecessary since it will be removed shortly. > }; > ... > }; > > struct net_iov { > enum net_iov_type type; > struct netmem_desc; This requires a huge change in a single commit since all the code referring to any of the page pool fields, struct net_iov, and maybe io_uring(?) should be altered at once. Plus, much more changes are required since struct netmem_desc would not overlay on struct page with what you suggest, which breaks the assumption that struct netmem_desc overlays on struct page in the current code. So at least, the work should be started once the code doesn't need the assumption. Thoughts? Byungchul > struct net_iov_area *owner; > } > > AFAICT, this should work..? > > -- > Thanks, > Mina