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[2003:d8:2f22:2e00:6e71:238a:de9f:e396]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f1ef0ab8sm102317135e9.13.2025.05.22.05.22.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 May 2025 05:22:33 -0700 (PDT) Message-ID: <99ae448a-5c5e-4491-8cf7-1325f47e225e@redhat.com> Date: Thu, 22 May 2025 14:22:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: reply: [RFC] pin_user_pages_fast failure count increased To: =?UTF-8?B?6buE5pyd6ZizIChaaGFveWFuZyBIdWFuZyk=?= , Hyesoo Yu , John Hubbard Cc: Jaewon Kim , "surenb@google.com" , "linux-mm@kvack.org" , =?UTF-8?B?5bq357qq5ruoIChTdGV2ZSBLYW5nKQ==?= , Zhaoyang Huang References: 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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: wZU8Z3Sb8Np-FfmJNH4xZBGSkXAzdTDgepAo7RyTuHw_1747916554 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 1BA8D180003 X-Stat-Signature: ryneyrcjkaoozqdsjfmw596j6b1fd4a5 X-Rspam-User: X-HE-Tag: 1747916556-310605 X-HE-Meta: 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 h7RW4weO 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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 22.05.25 12:18, 黄朝阳 (Zhaoyang Huang) wrote: >> On Mon, Apr 28, 2025 at 02:12:57PM -0700, John Hubbard wrote: >>> On 4/28/25 1:56 PM, David Hildenbrand wrote: >>>> On 28.04.25 22:14, John Hubbard wrote: >>>>> On 4/28/25 8:17 AM, Jaewon Kim wrote: >>>>>> Hi >>>>>> >>>>>> If pin_user_pages_fast does not pin all the requested number of >>>>>> pages, then drivers calling to pin_user_pages_fast should retry >>>>>> until the gup pins all? >>>>>> >>>>> >>>>> Approaches vary, for handling partial success of pin_user_pages(). >>>>> >>>>> * Many drivers unpin everything and either bail out entirely, or >>>>> retry pinning the entire original range. >>>> >>>> Hm, unpinning + trying to repin the entire range can easily result >>>> in an endless loop on persistent errors IIRC? >>>> >>> >>> I vaguely recall a limited number of retries, yes. >>> >>> thanks, >>> -- >>> John Hubbard >>> >>> >> >> Hi, >> >> I'd like to report a potential issue introduced by a recent change in >> 1aaf8c122918 mm: gup: fix infinite loop within __get_longterm_locked >> >> Previously, the call to migrate_longterm_unpinnable_folio() was guarded by the >> collected variable. This meant that if a CMA page was temporarily held in the >> pagevec and failed LRU isolation, it wouldn't be added to the >> movable_page_list, but the collected counter would still be incremented. Okay, so we'd also express that way "any longterm_pinnable page found". > There is lru_add_drain_all for dealing with this scenario, so this won't be the case, right? Good point. Only concurrent isolation might be problematic (concurrent reclaim?). >> >> As a result, migrate_longterm_unpinnable_folio() would return -EAGAIN, and >> the process would be retried until migration of the CMA page succeeded. >> >> However, in the recent patch merged into mainline, the logic now only checks >> whether movable_page_list is empty, and no longer relies on the collected >> count. >> This can cause CMA pages that fail isolation to bypass retry logic and remain >> pinned. >> >> Effectively,long-term pinning is now possible for CMA pages — something that >> previously would have been avoided through repeated attempts. Calling migrate_longterm_unpinnable_folios() when there is nothing to migrate is stupid. Maybe something like: diff --git a/mm/gup.c b/mm/gup.c index 329c5f7acc7a0..58b8e40fc19ed 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2301,14 +2301,15 @@ static void pofs_unpin(struct pages_or_folios *pofs) } /* - * Returns the number of collected folios. Return value is always >= 0. + * Returns whether any longterm unpinnable folio was found (if isolation + * fails, not all can be added to the movable_folio_list). */ -static void collect_longterm_unpinnable_folios( +static bool collect_longterm_unpinnable_folios( struct list_head *movable_folio_list, struct pages_or_folios *pofs) { + bool drain_allow = true, any_unpinnable = false; struct folio *prev_folio = NULL; - bool drain_allow = true; unsigned long i; for (i = 0; i < pofs->nr_entries; i++) { @@ -2320,6 +2321,7 @@ static void collect_longterm_unpinnable_folios( if (folio_is_longterm_pinnable(folio)) continue; + any_unpinnable = true; if (folio_is_device_coherent(folio)) continue; @@ -2342,6 +2344,8 @@ static void collect_longterm_unpinnable_folios( NR_ISOLATED_ANON + folio_is_file_lru(folio), folio_nr_pages(folio)); } + + return any_unpinnable; } /* @@ -2417,11 +2421,12 @@ migrate_longterm_unpinnable_folios(struct list_head *movable_folio_list, static long check_and_migrate_movable_pages_or_folios(struct pages_or_folios *pofs) { + bool any_unpinnable; LIST_HEAD(movable_folio_list); - collect_longterm_unpinnable_folios(&movable_folio_list, pofs); + any_unpinnable = collect_longterm_unpinnable_folios(&movable_folio_list, pofs); if (list_empty(&movable_folio_list)) - return 0; + return any_unpinnable ? -EAGAIN : 0; return migrate_longterm_unpinnable_folios(&movable_folio_list, pofs); } -- Cheers, David / dhildenb