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[2003:d8:2f22:2e00:6e71:238a:de9f:e396]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f1ef035csm105567615e9.11.2025.05.22.08.07.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 May 2025 08:08:00 -0700 (PDT) Message-ID: <1dd70770-f097-46bc-99b1-1bd3249032fb@redhat.com> Date: Thu, 22 May 2025 17:07:59 +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" , =?UTF-8?B?7Jyg7Zic7IiY?= , "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> <20250522144418epcms1p2a31c1a5c95b1937077bddf1b30495e83@epcms1p2> 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: <20250522144418epcms1p2a31c1a5c95b1937077bddf1b30495e83@epcms1p2> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: YtXa2ErqFRK6KH7S4cFI7I1ZG_aCQSI80lTTv_uOsVY_1747926482 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: rspam03 X-Rspamd-Queue-Id: DCE0AA0016 X-Stat-Signature: grxi7cc33861dxu8arncgs466dea1pa5 X-Rspam-User: X-HE-Tag: 1747926484-185020 X-HE-Meta: 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 j+iwcoZn 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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 16:44, κΉ€μž¬μ› wrote: >> 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. > > I did not understand. Do you mean we need to call pofs_unpin in case of any_unpinnable? At least that's what we did before 1aaf8c122 when calling collect_longterm_unpinnable_folios() I think. > I think your following code seems to be good to me. > return any_unpinnable ? -EAGAIN : 0; I think we have to call pofs_unpin() here. Assuming we always call migrate_longterm_unpinnable_folios() with a list now, we could drop the list_empty() check in there. -- Cheers, David / dhildenb