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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id cl3-20020a5d5f03000000b0033afd49cac7sm3390196wrb.43.2024.01.31.03.13.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 Jan 2024 03:13:06 -0800 (PST) Message-ID: Date: Wed, 31 Jan 2024 12:13:05 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 9/9] mm/memory: optimize unmap/zap with PTE-mapped THP To: Ryan Roberts , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Catalin Marinas , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Michael Ellerman , Christophe Leroy , "Naveen N. Rao" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Arnd Bergmann , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org References: <20240129143221.263763-1-david@redhat.com> <20240129143221.263763-10-david@redhat.com> <424115a2-a924-4c28-8027-32db6ab9278d@arm.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 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: <424115a2-a924-4c28-8027-32db6ab9278d@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 5DC2EC0016 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: dy51b14mdqn9mcq9ryjbam18nminzhei X-HE-Tag: 1706699590-567710 X-HE-Meta: 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 BsWWqFNN catHfq3r7QEyYMBPvG8nRpp3Z7PNf/TVivOUj6t6x0TxbB5llXaXN8D5hvhak3HadoHnxzTOomJ9cXyyAn4I+Q9W3FXureql9WkzCWClYGL118PEwSkVrrNJQw7gjSEqBetKqG9NWxRj4zNadiGKW8vZl168Ts3HNi8+iX94C31TTkfeq0aCU5MryVkOStsdFRMXa+NjAvIMJzQ44mBpBCXyenIYU7wz5ML6eJtolylH5N8se025rYckACyuG0tzAngwjaZnDq0hB76iGXuegOIDHKCN7cOdvHDengNdSsxM+BCvByH5h4TT8QQrZK6kRH0Jgrq+zJWUv4XWki+RQpMs6yN000ShZiCFig234Ev2u7H09XCRzPefroJ6CTzagr9JHU5aNASEKqkO5MpHeIcAmyP9ETxUXH9sZMdZY3SieW7l+3E65twBTIq5h3rGW3exe/WCtinc+r1WMkOF5SAYrHQ== 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: >>>> -        folio_remove_rmap_pte(folio, page, vma); >>>> +        folio_remove_rmap_ptes(folio, page, nr, vma); >>>> + >>>> +        /* Only sanity-check the first page in a batch. */ >>>>           if (unlikely(page_mapcount(page) < 0)) >>>>               print_bad_pte(vma, addr, ptent, page); >>> >>> Is there a case for either removing this all together or moving it into >>> folio_remove_rmap_ptes()? It seems odd to only check some pages. >>> >> >> I really wanted to avoid another nasty loop here. >> >> In my thinking, for 4k folios, or when zapping subpages of large folios, we >> still perform the exact same checks. Only when batching we don't. So if there is >> some problem, there are ways to get it triggered. And these problems are barely >> ever seen. >> >> folio_remove_rmap_ptes() feels like the better place -- especially because the >> delayed-rmap handling is effectively unchecked. But in there, we cannot >> "print_bad_pte()". >> >> [background: if we had a total mapcount -- iow cheap folio_mapcount(), I'd check >> here that the total mapcount does not underflow, instead of checking per-subpage] > > All good points... perhaps extend the comment to describe how this could be > solved in future with cheap total_mapcount()? Or in the commit log if you prefer? I'll add more meat to the cover letter, thanks! -- Cheers, David / dhildenb