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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tEIP8-000000071C3-2FUp; Fri, 22 Nov 2024 01:24:14 +0000 Date: Fri, 22 Nov 2024 01:24:14 +0000 From: Matthew Wilcox To: Abdiel Janulgue Cc: Boqun Feng , Alice Ryhl , rust-for-linux@vger.kernel.org, Miguel Ojeda , Alex Gaynor , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , Wedson Almeida Filho , Valentin Obst , open list , Andrew Morton , "open list:MEMORY MANAGEMENT" , airlied@redhat.com, Kairui Song Subject: Re: [PATCH v3 0/2] rust: page: Add support for existing struct page mappings Message-ID: References: <98a46b27-c4bb-4540-8f75-f176c3f2fae1@gmail.com> <650846e4-b6a0-472d-a14e-4357d20faadb@gmail.com> <0195fb77-c55a-40d5-8fe2-5844158f4f63@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0195fb77-c55a-40d5-8fe2-5844158f4f63@gmail.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 0F10140009 X-Stat-Signature: jyf8f43rgru8erituww8gge3opioufz8 X-Rspam-User: X-HE-Tag: 1732238622-81273 X-HE-Meta: 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 0NqgWe4X Tz96pGPcZq+ENLrvBeT0utNE1V2eZ5JlEvpZrhVZhim59QlPAmCpmBYQzMd5f2F0gaIe6oisl5i3lsyv/m/JPtqahJIT1Og+pTyWIUzlkLu0744hkAQwSiHLCV9aH23dTLyMrzlKKD7Bg81StaG1nlRqAxACVFfrDQKLRS9mLB6/Lnf6h1/YqphttEeqbdhZL5FafiDjznD6iDzR5Js8xduDedDiGdOO53IeE4rPZ7pb6sdtlsD9mZ/PMq0BTd/e0S2IRlmfovpKfWfBsvKLSEIy0nfMp8l1r8BNqGKT0ho/Dppg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Nov 22, 2024 at 01:18:28AM +0200, Abdiel Janulgue wrote: > We need an abstraction of struct page to construct a scatterlist which is > needed for an internal firmware structure. Now most of pages needed there > come from vmalloc_to_page() which, unlike the current rust Page abstraction, > not allocated on demand but is an existing mapping. > > Hope that clears things up! That's very helpful! So the lifetime of the scatterllist must not outlive the lifetime of the vmalloc allocation. That means you can call kmap_local_page() on the page in the scatterlist without worrying about the refcount of the struct page. BTW, you can't call page_address() on vmalloc memory because vmalloc can allocate pages from HIGHMEM. Unless you're willing to disable support for 32-bit systems with highmem ...