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[2003:cb:c733:7c00:d067:e327:4f99:7546]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431bd990dc1sm14201265e9.40.2024.10.30.01.34.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Oct 2024 01:34:52 -0700 (PDT) Message-ID: Date: Wed, 30 Oct 2024 09:34:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: restore the ability to pin more than 2GB at a time To: John Hubbard , Alistair Popple Cc: Christoph Hellwig , Andrew Morton , LKML , linux-mm@kvack.org, linux-stable@vger.kernel.org, Vivek Kasireddy , Dave Airlie , Gerd Hoffmann , Matthew Wilcox , Jason Gunthorpe , Peter Xu , Arnd Bergmann , Daniel Vetter , Dongwon Kim , Hugh Dickins , Junxiao Chang , Mike Kravetz , Oscar Salvador References: <20241030030116.670307-1-jhubbard@nvidia.com> <249d2614-0bcc-4ca8-b24e-7c0578a81dce@nvidia.com> <87r07yp0ng.fsf@nvdebian.thelocal> <128d04dd-2d48-4a98-8537-49589b4db1c3@nvidia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <128d04dd-2d48-4a98-8537-49589b4db1c3@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: D6E0840017 X-Stat-Signature: 64771katazksku7qjmeq3xaxkh8taggc X-Rspam-User: X-HE-Tag: 1730277262-692418 X-HE-Meta: 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 ouamw42M vexu8XEiaeCCjpIHc516f0DVAT1a9xxki40d1pT7czWxdBDaAtcKZOx3fd1acRUXcS0aY66TEN04YEftmOuz8veLoVYrwBhHQzUqZNM0zj2yNrLw1xZHuMkbx51/E+FkifcSoLwiL2UqP8JUN97H2ASd0jKGpxV1ucBBcld0VR1/K2GQGYxIsqxdBtMMNDv2Du+52+PZRmAhSNcpZCdQ+dLZwDu6a5PbbQC1QlMQWIrqwvR9jOwzSoJBcKnd/qJAAOyZQm3fvb3KHPRch4lbTYHg6H7RSs9m17fjJByhm8OmjonMIJN8C0Knfzm/SeKCrXh5zF8sRoJLFnqGJ2P30gc1H4iVhVhAqsQ4U1J0a1w8TRZCDSu7xjxmv1dXpkbfiwdMepQRniHqWofR7GCSo7Xi1JEfyZWqO7g95JzXAMfQPqrzHdk9zuWZYf8QSZe+1RSg12O+o5J3jGQE= 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 30.10.24 07:50, John Hubbard wrote: > On 10/29/24 11:18 PM, Alistair Popple wrote: >> John Hubbard writes: >>> On 10/29/24 9:42 PM, Christoph Hellwig wrote: >>>> On Tue, Oct 29, 2024 at 09:39:15PM -0700, John Hubbard wrote: > ... >>>> Because pinning down these amounts of memoryt is completely insane. >>>> I don't mind the switch to kvmalloc, but we need to put in an upper >>>> bound of what can be pinned. >>> >>> I'm wondering though, how it is that we decide how much of the user's >>> system we prevent them from using? :) People with hardware accelerators >>> do not always have page fault capability, and yet these troublesome >>> users insist on stacking their system full of DRAM and then pointing >>> the accelerator to it. >>> >>> How would we choose a value? Memory sizes keep going up... >> >> The obvious answer is you let users decide. I did have a patch series to >> do that via a cgroup[1]. However I dropped that series mostly because I >> couldn't find any users of such a limit to provide feedback on how they >> would use it or how they wanted it to work. >> > > Trawling through the discussion there, I see that Jason Gunthorpe mentioned: > > "Things like VFIO & KVM use cases effectively pin 90% of all system memory" The unusual thing is not the amount of system memory we are pinning but *how many* pages we try pinning in the single call. If you stare at vfio_pin_pages_remote, we seem to be batching it. long req_pages = min_t(long, npage, batch->capacity); Which is #define VFIO_BATCH_MAX_CAPACITY (PAGE_SIZE / sizeof(struct page *)) So you can fix this in your driver ;) We should maybe try a similar limit internally: if you call pin_user_pages_remote() with a large number, we'll cap it at some magic value (similar to above). The caller will simply realize that not all pages were pinned and will retry. See get_user_pages_remote(): "Returns either number of pages pinned (which may be less than the number requested), or an error. Details about the return value:" Alternatively, I recall there was a way to avoid the temporary allocation ... let me hack up a prototype real quick. -- Cheers, David / dhildenb