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[2003:cb:c747:ff00:9d85:4afb:a7df:6c45]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390cd86c93bsm6150565f8f.26.2025.02.26.08.52.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Feb 2025 08:52:14 -0800 (PST) Message-ID: <12dfdfde-06db-4112-9979-2ed320f80439@redhat.com> Date: Wed, 26 Feb 2025 17:52:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: fix finish_fault() handling for large folios To: Matthew Wilcox Cc: Brian Geffon , Andrew Morton , Zi Yan , Kefeng Wang , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Baolin Wang , Hugh Dickins , Marek Maslanka References: <20250226114815.758217-1-bgeffon@google.com> <121abab9-5090-486b-a3af-776a9cae04fb@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ZjYDKJUpP5YTyDHdS1iVI6Vpw568fzKNGn9k4bdQBY4_1740588735 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: 88B5D80004 X-Stat-Signature: mbxj4zbp1je7stuef7hh8abda5y4xac3 X-Rspam-User: X-HE-Tag: 1740588740-354928 X-HE-Meta: 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 OiKQey/7 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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 26.02.25 17:28, Matthew Wilcox wrote: > On Wed, Feb 26, 2025 at 04:42:46PM +0100, David Hildenbrand wrote: >> On 26.02.25 15:03, Matthew Wilcox wrote: >>> On Wed, Feb 26, 2025 at 06:48:15AM -0500, Brian Geffon wrote: >>>> When handling faults for anon shmem finish_fault() will attempt to install >>>> ptes for the entire folio. Unfortunately if it encounters a single >>>> non-pte_none entry in that range it will bail, even if the pte that >>>> triggered the fault is still pte_none. When this situation happens the >>>> fault will be retried endlessly never making forward progress. >>>> >>>> This patch fixes this behavior and if it detects that a pte in the range >>>> is not pte_none it will fall back to setting just the pte for the >>>> address that triggered the fault. >>> >>> Surely there's a similar problem in do_anonymous_page()? >> >> I recall we handle it in there correctly the last time I stared at it. >> >> We check pte_none to decide which folio size we can allocate (including >> basing the decision on other factors like VMA etc), and after retaking the >> PTL, we recheck vmf_pte_changed / pte_range_none() to make sure there were >> no races. > > Ah, so then we'll retry and allocate a folio of the right size the next > time? IIRC we'll retry the fault in case we had a race. Likely, if we had a race, somebody else installed a (large) folio and we essentially have to second fault. If, for some reason, the race only touched parts of the PTEs we tried to modify, we'll get another fault and allocate something (smaller) that would fit into the new empty range. So yes, we're more flexible because we're allocating the folios and don't have to take whatever folio size is in the pagecache in consideration. -- Cheers, David / dhildenb