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[2003:cb:c71e:bf00:eba1:3ab9:ab0f:d676]) by smtp.gmail.com with ESMTPSA id k6-20020a05600c478600b004185be4baefsm4614042wmo.0.2024.05.01.23.56.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 May 2024 23:56:29 -0700 (PDT) Message-ID: <92289167-5655-4c51-8dfc-df7ae53fdb7b@redhat.com> Date: Thu, 2 May 2024 08:56:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] RDMA/umem: pin_user_pages*() can temporarily fail due to migration glitches To: Alistair Popple , Jason Gunthorpe Cc: Christoph Hellwig , John Hubbard , Andrew Morton , LKML , linux-rdma@vger.kernel.org, linux-mm@kvack.org, Mike Marciniszyn , Leon Romanovsky , Artemy Kovalyov , Michael Guralnik , Pak Markthub References: <20240501003117.257735-1-jhubbard@nvidia.com> <20240501121032.GA941030@nvidia.com> <87r0el3tfi.fsf@nvdebian.thelocal> 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: <87r0el3tfi.fsf@nvdebian.thelocal> 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: rspam07 X-Rspamd-Queue-Id: C029B40009 X-Stat-Signature: a4yh11cyetfh9bijcw3i7u8xk78ncesm X-Rspam-User: X-HE-Tag: 1714632993-429177 X-HE-Meta: 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 OgdkGrwL 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 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 02.05.24 03:05, Alistair Popple wrote: > > Jason Gunthorpe writes: > >> On Tue, Apr 30, 2024 at 10:10:43PM -0700, Christoph Hellwig wrote: >>>> + pinned = -ENOMEM; >>>> + int attempts = 0; >>>> + /* >>>> + * pin_user_pages_fast() can return -EAGAIN, due to falling back >>>> + * to gup-slow and then failing to migrate pages out of >>>> + * ZONE_MOVABLE due to a transient elevated page refcount. >>>> + * >>>> + * One retry is enough to avoid this problem, so far, but let's >>>> + * use a slightly higher retry count just in case even larger >>>> + * systems have a longer-lasting transient refcount problem. >>>> + * >>>> + */ >>>> + static const int MAX_ATTEMPTS = 3; >>>> + >>>> + while (pinned == -EAGAIN && attempts < MAX_ATTEMPTS) { >>>> + pinned = pin_user_pages_fast(cur_base, >>>> + min_t(unsigned long, >>>> + npages, PAGE_SIZE / >>>> + sizeof(struct page *)), >>>> + gup_flags, page_list); >>>> ret = pinned; >>>> - goto umem_release; >>>> + attempts++; >>>> + >>>> + if (pinned == -EAGAIN) >>>> + continue; >>>> } >>>> + if (pinned < 0) >>>> + goto umem_release; >>> >>> This doesn't make sense. IFF a blind retry is all that is needed it >>> should be done in the core functionality. I fear it's not that easy, >>> though. >> >> +1 >> >> This migration retry weirdness is a GUP issue, it needs to be solved >> in the mm not exposed to every pin_user_pages caller. >> >> If it turns out ZONE_MOVEABLE pages can't actually be reliably moved >> then it is pretty broken.. > > I wonder if we should remove the arbitrary retry limit in > migrate_pages() entirely for ZONE_MOVEABLE pages and just loop until > they migrate? By definition there should only be transient references on > these pages so why do we need to limit the number of retries in the > first place? There are some weird things that still needs fixing: vmsplice() is the example that doesn't use FOLL_LONGTERM. -- Cheers, David / dhildenb