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[2003:d8:2f07:dd00:ca9c:199e:d2b6:9099]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-464eadd7e11sm26175745e9.0.2025.09.17.23.00.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Sep 2025 23:00:12 -0700 (PDT) Message-ID: <17d1b293-e393-4989-a357-7eea74b3c805@redhat.com> Date: Thu, 18 Sep 2025 08:00:11 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] mm: vmscan: remove folio_test_private() check in pageout() To: Baolin Wang , akpm@linux-foundation.org, hannes@cmpxchg.org Cc: mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, hughd@google.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <9ef0e560dc83650bc538eb5dcd1594e112c1369f.1758166683.git.baolin.wang@linux.alibaba.com> From: David Hildenbrand Content-Language: en-US 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: <9ef0e560dc83650bc538eb5dcd1594e112c1369f.1758166683.git.baolin.wang@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 18.09.25 05:46, Baolin Wang wrote: > The folio_test_private() check in pageout() was introduced by commit > ce91b575332b ("orphaned pagecache memleak fix") in 2005 (checked from > a history tree[1]). As the commit message mentioned, it was to address > the issue where reiserfs pagecache may be truncated while still pinned. > To further explain, the truncation removes the page->mapping, but the > page is still listed in the VM queues because it still has buffers. > > In 2008, commit a2b345642f530 ("Fix dirty page accounting leak with ext3 > data=journal") seems to be dealing with a similar issue, where the page > becomes dirty after truncation, and it provides a very useful call stack: > truncate_complete_page() > cancel_dirty_page() // PG_dirty cleared, decr. dirty pages > do_invalidatepage() > ext3_invalidatepage() > journal_invalidatepage() > journal_unmap_buffer() > __dispose_buffer() > __journal_unfile_buffer() > __journal_temp_unlink_buffer() > mark_buffer_dirty(); // PG_dirty set, incr. dirty pages > > In this commit a2b345642f530, we forcefully clear the page's dirty flag > during truncation (in truncate_complete_page()). > > Now it seems this was just a peculiar usage specific to reiserfs. Maybe > reiserfs had some extra refcount on these pages, which caused them to pass > the is_page_cache_freeable() check. With the fix provided by commit a2b345642f530 > and reiserfs being removed in 2024 by commit fb6f20ecb121 ("reiserfs: The > last commit"), such a case is unlikely to occur again. So let's remove the > redundant folio_test_private() checks and related buffer_head release logic, > and just leave a warning here to catch such a bug. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git > Acked-by: David Hildenbrand > Acked-by: Shakeel Butt > Signed-off-by: Baolin Wang > --- > mm/vmscan.c | 12 +++--------- > 1 file changed, 3 insertions(+), 9 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f1fc36729ddd..930add6d90ab 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -701,16 +701,10 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping, > return PAGE_KEEP; > if (!mapping) { > /* > - * Some data journaling orphaned folios can have > - * folio->mapping == NULL while being dirty with clean buffers. > + * Is it still possible to have a dirty folio with > + * a NULL mapping? I think not. > */ I would rephrase slightly (removing the "I think not"): /* * We should no longer have dirty folios with clean buffers and a NULL * mapping. However, let's be careful for now. */ > - if (folio_test_private(folio)) { > - if (try_to_free_buffers(folio)) { > - folio_clear_dirty(folio); > - pr_info("%s: orphaned folio\n", __func__); > - return PAGE_CLEAN; > - } > - } > + VM_WARN_ON_FOLIO(true, folio); > return PAGE_KEEP; > } > -- Cheers David / dhildenb