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[2003:cb:c72e:e400:431d:9c08:5611:693c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-437c74c475csm212212335e9.20.2025.01.20.11.02.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2025 11:02:01 -0800 (PST) Message-ID: Date: Mon, 20 Jan 2025 20:01:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] s390: Remove PageDirty check inside mk_pte() To: Alexander Gordeev , "Matthew Wilcox (Oracle)" Cc: Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Claudio Imbrenda , Christian Borntraeger , linux-mm@kvack.org References: <20250116212338.653160-1-willy@infradead.org> 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: RQNWh5Hd_FtC0v7k6PDywrWi_dMe5-YDMFC9rKBvx30_1737399723 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: rspam05 X-Rspamd-Queue-Id: CD64B10001A X-Stat-Signature: izbkjgntxepgat4rhf3e81axop481o3m X-Rspam-User: X-HE-Tag: 1737399725-246676 X-HE-Meta: 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 1GZlKJTb Cs9RHfbR2PyFIJszrPMyuCBZU/v4m9MQp6EC+tBm+QqdZ4zOGlIkmkcoFf1J4EcCBUoAYRBUeTiB9rdP+G1IlGT50wU2HrdLyLTD/vS/WHIwQgVQelJRC17wGhwA0h3ZNjlj7I0M+7l6kBIPZ++woKseIfa+kYj1VWINkRr5dJ7E8bkTlMgiorY3+BDPAJOkgvaE7jcJ/mjLVLtaUCHhpC9ZCa4gi/V69wBq4GSfkB+aWqeKp9O2q0ZPScxrmPyQxZ6gZ9IJyyxv9FB/gTpvHcyB3+vgx9qrTSD8BVW/dIKlykrcNfpr9t2/8YABQ7TTKfl/Ej1+uQ7+APRReOdMCib5wuxSJIfLwqlqC/36K148teEUnvP8aDUKW5tFFRo7oqbUuxpoiuaG5q3PRbrj8b/QuXPyHRUd8CztSnbQ1Dk/mKY79FMWHHyIM4OHCN9X5lY2xrbtEzfHfycP4r64fpISiKEt2T9N//8/DjeSnryuNqXqj3lhWb2MGogVPBTkPuYmM6oYFjSn+vUCuHc/Re7iqvA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000027, 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 20.01.25 17:39, Alexander Gordeev wrote: > On Thu, Jan 16, 2025 at 09:23:36PM +0000, Matthew Wilcox (Oracle) wrote: > > Hi Matthew, > >> In commit abf09bed3cce ("s390/mm: implement software dirty bits"), >> the rationale for adding the PageDirty() test was: >> >> To avoid an excessive number of additional faults the >> mk_pte primitive checks for PageDirty if the pgprot value >> allows for writes and pre-dirties the pte. That avoids all >> additional faults for tmpfs and shmem pages until these >> pages are added to the swap cache. >> >> shmem does not mark newly allocated folios as dirty since 2016 (commit >> 75edd345e8ed) so this test has been ineffective since then. It still >> triggers for some calls to mk_pte(), but those calls are usually >> followed with other calls to pte_mkdirty() making the ones inside >> s390's mk_pte() redundant. >> >> Signed-off-by: Matthew Wilcox (Oracle) >> --- >> arch/s390/include/asm/pgtable.h | 5 +---- >> 1 file changed, 1 insertion(+), 4 deletions(-) >> >> Please check this doesn't cause any real world performance issues. >> Alexander and I briefly discussed this last year: >> https://lore.kernel.org/linux-mm/20240814154427.162475-5-willy@infradead.org/ >> but then I missed his followup on August 22nd, and thought it best to >> reopen the conversation with a fresh patch to test. > > I tried to take exactly this approach last year, but dropped the ball. > > Despite the commit 75edd345e8ed claim above I still observed that a read > access to shmem page could end up in creation of a dirty PTE: > > handle_pte_fault() -> do_pte_missing() -> do_fault() -> > do_read_fault() -> finish_fault() -> set_pte_range() -> mk_pte() Could we perform the dirty-setting on that level, the caller of mk_pte()? -- Cheers, David / dhildenb