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imf07.hostedemail.com; dkim=none; spf=pass (imf07.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=1752640051; a=rsa-sha256; cv=none; b=5HeCPfmZEnsNbCtOZIo2qfaQd+lexkzcfixmztGk7GGg5fpm+MFB4F0f+94W1rbHgG83Ms 9G7H78t4yYzx7PPpUs0baWDn4RfcpQRP8nJKnlMoAQjqKKmiJf3mkT+30gUUURDAMc2jOW 9itAcRbjgH4/pOt9z1R3QjqdIeYCfEM= X-AuditID: a67dfc5b-669ff7000002311f-fe-68772a2f6dda Date: Wed, 16 Jul 2025 13:27:22 +0900 From: Byungchul Park To: Pavel Begunkov Cc: Mina Almasry , willy@infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel_team@skhynix.com, ilias.apalodimas@linaro.org, harry.yoo@oracle.com, akpm@linux-foundation.org, andrew+netdev@lunn.ch, toke@redhat.com, david@redhat.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-rdma@vger.kernel.org, bpf@vger.kernel.org, vishal.moola@gmail.com, hannes@cmpxchg.org, ziy@nvidia.com, jackmanb@google.com, wei.fang@nxp.com, shenwei.wang@nxp.com, xiaoning.wang@nxp.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, anthony.l.nguyen@intel.com, przemyslaw.kitszel@intel.com, sgoutham@marvell.com, gakula@marvell.com, sbhatta@marvell.com, hkelam@marvell.com, bbhushan2@marvell.com, tariqt@nvidia.com, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, saeedm@nvidia.com, leon@kernel.org, mbloch@nvidia.com, danishanwar@ti.com, rogerq@kernel.org, nbd@nbd.name, lorenzo@kernel.org, ryder.lee@mediatek.com, shayne.chen@mediatek.com, sean.wang@mediatek.com, matthias.bgg@gmail.com, angelogioacchino.delregno@collabora.com, aleksander.lobakin@intel.com, horms@kernel.org, m-malladi@ti.com, krzysztof.kozlowski@linaro.org, matthias.schiffer@ew.tq-group.com, robh@kernel.org, imx@lists.linux.dev, intel-wired-lan@lists.osuosl.org, linux-arm-kernel@lists.infradead.org, linux-wireless@vger.kernel.org, linux-mediatek@lists.infradead.org Subject: Re: [PATCH net-next v10 02/12] netmem: use netmem_desc instead of page to access ->pp in __netmem_get_pp() Message-ID: <20250716042722.GA12760@system.software.com> References: <20250714120047.35901-1-byungchul@sk.com> <20250714120047.35901-3-byungchul@sk.com> <9bed2f6e-6251-4d0c-ad1e-f1b8625a0a10@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; 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> > > + > > > + /* XXX: How to extract netmem_desc from page must be changed, > > > + * once netmem_desc no longer overlays on page and will be > > > + * allocated through slab. > > > + */ > > > + return (struct netmem_desc *)page; > > > +} > > > + > > > > Same thing. Do not create a generic looking pp_page_to_nmdesc helper > > which does not check that the page is the correct type. The > > DEBUG_NET... is not good enough. > > > > You don't need to add a generic helper here. There is only one call > > site. Open code this in the callsite. The one callsite is marked as > > unsafe, only called by code that knows that the netmem is specifically > > a pp page. Open code this in the unsafe callsite, instead of creating > > a generic looking unsafe helper and not even documenting it's unsafe. > > > > > /** > > > * __netmem_get_pp - unsafely get pointer to the &page_pool backing @netmem > > > * @netmem: netmem reference to get the pointer from > > > @@ -280,7 +291,7 @@ static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem) > > > */ > > > static inline struct page_pool *__netmem_get_pp(netmem_ref netmem) > > > { > > > - return __netmem_to_page(netmem)->pp; > > > + return pp_page_to_nmdesc(__netmem_to_page(netmem))->pp; > > > } > > > > This makes me very sad. Casting from netmem -> page -> nmdesc... > > The function is not used, and I don't think the series adds any That's whay I'd been keeping the patch, 'netmem: remove __netmem_get_pp()' until v6 [1]. [1] https://lore.kernel.org/all/20250620041224.46646-7-byungchul@sk.com/ However, as the following change log described [2], I excluded the patch from v7 since __netmem_get_pp() started to be used again by libeth. [2] https://lore.kernel.org/all/20250625043350.7939-1-byungchul@sk.com/ > new users? It can be killed then. It's a horrible function anyway, > would be much better to have a variant taking struct page * if > necessary. > > > Instead, we should be able to go from netmem directly to nmdesc. I > > would suggest rename __netmem_clear_lsb to netmem_to_nmdesc and have > > it return netmem_desc instead of net_iov. Then use it here. > > Glad you liked the diff I suggested :) In either case, seems > like it's not strictly necessary for this iteration as > __netmem_get_pp() should be killed, and the rest of patches work > directly with pages. Killing __netmem_get_pp() would be the best I think. Byungchul > > > > We could have an unsafe version of netmem_to_nmdesc which converts the > > netmem to netmem_desc without clearing the lsb and mark it unsafe. > > > > -- > Pavel Begunkov