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[2003:d8:2f22:2e00:6e71:238a:de9f:e396]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a3648baa6asm20964738f8f.91.2025.05.22.07.06.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 May 2025 07:06:49 -0700 (PDT) Message-ID: Date: Thu, 22 May 2025 16:06:48 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: reply: [RFC] pin_user_pages_fast failure count increased To: jaewon31.kim@samsung.com, "zhaoyang.huang@unisoc.com" , Hyesoo Yu , "jhubbard@nvidia.com" , "surenb@google.com" , "Steve.Kang@unisoc.com" , "huangzhaoyang@gmail.com" Cc: Jaewon Kim , "linux-mm@kvack.org" References: <99ae448a-5c5e-4491-8cf7-1325f47e225e@redhat.com> <20250522130901epcms1p31d757b179fbb3563cad6bef4a1829235@epcms1p3> 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: <20250522130901epcms1p31d757b179fbb3563cad6bef4a1829235@epcms1p3> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: GUUBZJAlJ_hiUhfzNaJmx6v5pcrKym2DFVdE1EWIKI0_1747922811 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: B279F8000C X-Stat-Signature: 9r35o4fhcmwz5uatrx3mcwyt8hj8yik1 X-Rspam-User: X-HE-Tag: 1747922814-723902 X-HE-Meta: U2FsdGVkX19Gzha/xNEkmdWtb62lDnJrIcMqckXcdZsXDmhMz3R3uIkMOboQP+LqkVW8y8OdSiVORtOxK0zTTYSQ+y+jxMx4dPOBMp353DgX2TgU/iIULByX3eDzkJTYBk54dxL18Yt36yb7CJiWB4sHZ8oE1RRI8A/KDtuw9+0TK3DtBIYS8cd/5uYDcitoLX/bWMkEJUrQteFUPS43eFg6YZ0YAj+Kdyf/gHcLiD+vwAqdKeHFh5o5v+bWbwgsgbPND+Q6eEPcdojLY3RkwE/cOtnMktZp+YaVWITxWJ8L4Ne27MHVJ2qYKVDJfDndLplpK8nqVQ0eDNgjrkHr4mANn9ivFc23QdWSoHNJYwbKBU/37HoHSDOhqEMkbYBn2itAhsAbkglYQPhAWc/Y/7gX/Mn8lQDrT6au0VZFGdl49USDO579DUNT1i3sm9VGsoLWPVpZREUTNPmeTAC10Ue4GIT0midwwX9Of0IVe54zo+mw4gFrSDnEoGlceHN4eYz/VoJakhiz36+lXa89gBDqCSZT3trkH6/a6b7pWCikviO7vDWNhAbW3txRK4fauRDlPyJsN9YXzzPmGIGDiD7NIKpfkJsHCgEzQ6s8znc5slbBup6ZAWtPhB1RGkhgBe/2MTZHj2kJFR/nvc63DJ68T0DsJVbGdTpX4y55eX6Nt5d9Cv6glG/uGImlvZVUHzsRcGNftgbbZa9db+QME7N5fTk0Lyc4712Edi+TkPuLOsk1Tovuw4gKDzGN/cZVodzea6wc+zuyP/sj6A9yT7HKYWhfob3tbhstXL1BiU2yWtcRuyLD0Et7oUmaDgahA3WH474iSQQ94qH2j4dt7zw4G5GxsTB1ULY9fgD0hFN2a1igqrE7LX8+36FLk0g2JiIoOvxUb9IIDT0M5+wa/edGLLVNFIyrPV5AnqNNtGqv0dT4BltRD2PsUaXZVoEHXlNAGnBIpnslGVdWr3B /AF6chbp otYsnOtpFQOOSLEYIk0arWFwo2ycISAz1ZeyA8nR3UtPpTuc4bK3jREVC0lopuywJ653iw2S6p/l8y0OEZUSQ2yvgrnQeHl0BPNmZpbXuacGAStjSEJMdIiFOblqWYhU1+SsGaDQVWbuaYzZ8ncd/jLrdrZPf3cmG6+0V/FXnkaXONe5oXlbtMatrNFJAU8KUcE0fpOPTRF0bgF4q1SkKqDGIR5eVYQ6W9XlcMDZ1Q+HPqEE= 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 15:09, Jaewon Kim wrote: >> On 22.05.25 12:18, ?朝? (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 > > Hi > > Thank you for your comment and patch. > By the way, what if there are any_unpinnable pages and also pages in the movable_folio_list, > but migrate_longterm_unpinnable_folios failed to migrate and return other erros instead of -EAGAIN? > In that case, I think the CMA or other unpinnable pages would be pinned. Oh, I think what we have to do is call pofs_unpin(pofs)() in case we return with -EAGAIN early. That's what migrate_longterm_unpinnable_folios() would do. If we happen to call migrate_longterm_unpinnable_folios(), it would already unpin all folios by calling pofs_unpin(pofs). So we can just return whatever error we actually saw. Do you have the capacity to send a proper fix? -- Cheers, David / dhildenb