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b=OMEHcZskZbsd9sNyePcfeVaP4LOngwAbTIC83XAxZ0tD9OLeeABRkDku2fuk0g+y1 vstwxk+/WhMNWC4TKaJKBgVr2tlhJXr8haGlDj+OOWbpwHcqLVLpM2JSWcocgfM36d HLmybkPMy9ZN7sn4pjH3nT3ZPU7em7QOZfiDKF4RONrF1zS36XPL5OKSnUO/ssNOeC pS+ILw0MfO9dd3fEWa2rCS0SnBmB2tQspRAuCzajsGzLB4XsyHpeL5xuk7z/UfLkn2 7SuletPW9yxvfC/foN7weNDFmUfGCQLHJqaM3/IweckoYiTFcZQvuwWN4OMOOGd+bN Hfz2vMMkXxzaA== Message-ID: Date: Wed, 10 Jun 2026 15:18:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC v1] io_uring/rsrc: add fast path huge page handling in buffer registration To: Christoph Hellwig Cc: sw.prabhu6@gmail.com, axboe@kernel.dk, io-uring@vger.kernel.org, linux-kernel@vger.kernel.org, dave@stgolabs.net, dongjoo.seo1@samsung.com, Swarna Prabhu , "linux-mm@kvack.org" , Matthew Wilcox , Zi Yan References: <20260608062937.804758-1-sw.prabhu6@gmail.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 666EF1C0003 X-Stat-Signature: jm9oj7rugjn85s67t6ecy87asi5rqufh X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1781097538-96232 X-HE-Meta: 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 G1YkdN57 AZrrIKqKTeFsloyQ/deXyE+PHpyQA0tbiBHCkuq5MKoIcqfvKeLsYlrsTU8OxwFGTZIhfJ8i1erShv/zS2wrY+TRbyb4x+8oFDysQ+rhOFL9Y0pDEQH49yOM3nusnRPA0VdzLq4He7sz26mPEt2z+rxJKUoNNodWNM/p5CSbvzhL/KiizgRvZHaNihP+R8/aB0/lkjfeHsRqxNfxFsH5Co9iB0acU7Yi2kIOSdIExtf7UP8Egk701RgCnMj4XwAKPq7RBb6w/amIHUPEmnLN3OwxqGPaIsdSMIhsHGEcZEAifKIUsLMiiDEjybrG6C+di0F8DfuiwVkHaZU8OSkSpX/w+qTU4rx0kuft9xfPYF5Oz5Y0Kv5dc/vgA9+hurPqFms4uNgXvVeRLgjqQ3AhMdp2n3PcCcAtlzHpiQsWoLe92uqE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/10/26 13:34, Christoph Hellwig wrote: > On Wed, Jun 10, 2026 at 11:54:01AM +0200, David Hildenbrand (Arm) wrote: >>> Yes. iov_iter_extract_bvecs and thus the block direct I/O fast path >>> would instantly benefit from that. >> The tricky bit for such an interface is that, soon, some pages won't be folios, >> but we could still end up with non-folio pages in the address space (e.g., >> vm_insert_page()) and have to pin+return them. So using folios is not future-proof. > > I'm still doubtful on the "soon" beause of all the issues like this > in the I/O path. Yeah, there are a bunch of very hairy things. > >> There are some long-term plans on providing an interface that would abstract how >> you refcount something you GUP'ed. (because, some pages we GUP in the future >> might not even have a dedicated refcount, all still fairly unclear). But it's >> all not really finalized I think. >> >> For now, we could expose a folio+page/offset+nr_pages interface, where we, >> long-term, would not be able to return non-folio pages (e.g., vm_insert_page()) >> and would instead, in the future, fail the request if we stumble over a >> non-folio thing in the page tables. That sounds reasonable for now. > > I think whatever we're going to use for direct I/O has to also support > non-folio pages, especially PCI P2P memory. So coming up with an > interface that support this ASAP would be helpful. Yes. I think we can keep returning pages as long a the unpin interface knows the right thing to do to unpin them. > >> Another solution would be, exposing page-ranges (e.g., page + nr_pages), whereby >> we'd say, that all pages in a range belong to the same compound page, and that >> we took a single reference for all pages in the range. IOW, page_folio() would >> for now be the same for all pages in a range. > > This does sound like a reasonable short-term improvement. Right, and as long as callers don't cast the returned thing to a folio, it would be future proof. But I guess quite some GUP users cast to folios. Would there be users for a new interface that returns page ranges as described above, that would want to still unpin stuff partially? E.g., we give them a page range that belongs to the same folio with only a single pin/reference, but they would want to logically split that range and unpin pages individually? -- Cheers, David