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[2003:d8:2f25:700:d846:15f3:6ca0:8029]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e74893acecsm4580959f8f.36.2025.09.08.07.08.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 08 Sep 2025 07:08:05 -0700 (PDT) Message-ID: <1f714ba0-cdda-4122-b6a1-e1e0ea44b1f2@redhat.com> Date: Mon, 8 Sep 2025 16:08:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/7] mm/gup: check ref_count instead of lru before migration To: Hugh Dickins Cc: Andrew Morton , Will Deacon , Shivank Garg , Matthew Wilcox , Christoph Hellwig , Keir Fraser , Jason Gunthorpe , John Hubbard , Frederick Mayle , Peter Xu , "Aneesh Kumar K.V" , Johannes Weiner , Vlastimil Babka , Alexander Krabler , Ge Yang , Li Zhe , Chris Li , Yu Zhao , Axel Rasmussen , Yuanchu Xie , Wei Xu , Konstantin Khlebnikov , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <47c51c9a-140f-1ea1-b692-c4bae5d1fa58@google.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: nINWofDeYLIckVdYJ9oiVhhNaJwTR1OP3q9CNfbFsFo_1757340487 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: rspam02 X-Rspamd-Queue-Id: DE4CD1A0009 X-Stat-Signature: 5g6nriirxiomk6kg77qqo9cf38jqjkri X-Rspam-User: X-HE-Tag: 1757340489-641163 X-HE-Meta: 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 jHfqprJ9 lZHcxbxb/gLAu3ONYGXIXQYEmnvX5UmLmNuSPiftBKoS3md1fr3DtfKVVl0KUplnnKQJoVgiVbEai3b7sjynEB7xS4Dc/PekJEx89PzRgE89/SINy8ryohZaGen9fonP+t/4HEFGzLBOw2dEKjmGz5W4xX+MyQGFCOzEhKDtf15J7h0v4F2NiYbXin5HQHdDzE004IFgKofOvCUIG2U0EYWJm5a8Fv7rwvFatMIcgBwrYOSlp6b0XJxKUA/X8q8qbpkDMqqKruyboxwljVYC+xSvBRB+eocd1ZAiXhbBIA8RCMSaVL0yxkFGiSyV8v1eIdiAsg9EGq9viauFDoc3If5mxrzJw4U+1nnNWHohx4d/F0R+VmoOKh8AB/6PvKRQyQF3vsk6XTcfNQyJUZ70Q5O50LtrFUzYPRQebxMieFD+1i6TMh2NeVY0LG15LVOlDL268nqVZSB1WDO8goEs3Xqz13Q== 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 08.09.25 12:40, Hugh Dickins wrote: > On Mon, 1 Sep 2025, David Hildenbrand wrote: >> On 31.08.25 11:05, Hugh Dickins wrote: >>> diff --git a/mm/gup.c b/mm/gup.c >>> index adffe663594d..82aec6443c0a 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -2307,7 +2307,8 @@ static unsigned long >>> collect_longterm_unpinnable_folios( >>> continue; >>> } >>> - if (!folio_test_lru(folio) && drain_allow) { >>> + if (drain_allow && folio_ref_count(folio) != >>> + folio_expected_ref_count(folio) + 1) { >>> lru_add_drain_all(); >>> drain_allow = false; >>> } >> >> In general, to the fix idea >> >> Acked-by: David Hildenbrand > > Thanks, but I'd better not assume that in v2, even though code the same. > Will depend on how you feel about added paragraph in v2 commit message. > >> >> But as raised in reply to patch #1, we have to be a bit careful about >> including private_2 in folio_expected_ref_count() at this point. >> >> If we cannot include it in folio_expected_ref_count(), it's all going to be a >> mess until PG_private_2 is removed for good. >> >> So that part still needs to be figured out. > > Here's that added paragraph: > > Note on PG_private_2: ceph and nfs are still using the deprecated > PG_private_2 flag, with the aid of netfs and filemap support functions. > Although it is consistently matched by an increment of folio ref_count, > folio_expected_ref_count() intentionally does not recognize it, and ceph > folio migration currently depends on that for PG_private_2 folios to be > rejected. New references to the deprecated flag are discouraged, so do > not add it into the collect_longterm_unpinnable_folios() calculation: > but longterm pinning of transiently PG_private_2 ceph and nfs folios > (an uncommon case) may invoke a redundant lru_add_drain_all(). Would we also loop forever trying to migrate these folios if they reside on ZONE_MOVABLE? I would assume that is already the case, that migration will always fail due to the raised reference. -- Cheers David / dhildenb