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[2003:cb:c749:6600:b73a:466c:e610:686]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c8acb17sm1791950f8f.97.2024.12.19.07.47.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 07:47:19 -0800 (PST) Message-ID: Date: Thu, 19 Dec 2024 16:47:18 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/5] mm/migrate: skip migrating folios under writeback with AS_WRITEBACK_INDETERMINATE mappings To: Shakeel Butt Cc: Joanne Koong , miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, bernd.schubert@fastmail.fm, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Zi Yan , Oscar Salvador , Michal Hocko References: <20241122232359.429647-1-joannelkoong@gmail.com> <20241122232359.429647-5-joannelkoong@gmail.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: ChIy09hCyCd_95YRJ1leDpN0R-RHzZvCl30WjroBZck_1734623241 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: rspam10 X-Rspamd-Queue-Id: DC1FF180019 X-Stat-Signature: pnehzz9cxjgn3wsbccw39hzna4ctzbko X-Rspam-User: X-HE-Tag: 1734623209-516830 X-HE-Meta: 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 eEKYTr57 eBg7we6owxhjQIwknUAhkBuHGyv4F8vvs0My9sKV51j/EAFa9Sf8+7yNSJZXkDIKbJ0viFBiECBLKJxv3AGUdUAKKCHcVzF4yJsD9A0DUaM+iBO4NTJZ1TTWqDz20H2VNGNfhbLjK9ao3casSxX1NulLEhbf/12zph84RMsrX7w9rRl8U9nE1YZUVPkJgkE+05dl4o5OxxjnrJHzwdlfjA7uj2t3A4lYRcSojP7kBkbnvZM+/B+OWJaUTnKrMoIJUCIUPYmO5plTvkdnf2OaadbzJ11y5lUQwH2AOqqA7Zd5Zf9rE/haH3F0F9iqRu4RJ8eSTlFWQc6p1KPeBwuAbDddnqUZaOblsN1S83Fr+sRWCmv/XoQVxTkFVjSkDrFMeBCgTvU0seHPe0PBmJ1mmrcOdwBgcY1DXgwcI8Y6tH96U8JqZHqpWZ255bpNLkCtdDGh5VoSNYqRpUfZ/qoMb25zarg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000069, 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 19.12.24 16:43, Shakeel Butt wrote: > On Thu, Dec 19, 2024 at 02:05:04PM +0100, David Hildenbrand wrote: >> On 23.11.24 00:23, Joanne Koong wrote: >>> For migrations called in MIGRATE_SYNC mode, skip migrating the folio if >>> it is under writeback and has the AS_WRITEBACK_INDETERMINATE flag set on its >>> mapping. If the AS_WRITEBACK_INDETERMINATE flag is set on the mapping, the >>> writeback may take an indeterminate amount of time to complete, and >>> waits may get stuck. >>> >>> Signed-off-by: Joanne Koong >>> Reviewed-by: Shakeel Butt >>> --- >>> mm/migrate.c | 5 ++++- >>> 1 file changed, 4 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/migrate.c b/mm/migrate.c >>> index df91248755e4..fe73284e5246 100644 >>> --- a/mm/migrate.c >>> +++ b/mm/migrate.c >>> @@ -1260,7 +1260,10 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, >>> */ >>> switch (mode) { >>> case MIGRATE_SYNC: >>> - break; >>> + if (!src->mapping || >>> + !mapping_writeback_indeterminate(src->mapping)) >>> + break; >>> + fallthrough; >>> default: >>> rc = -EBUSY; >>> goto out; >> >> Ehm, doesn't this mean that any fuse user can essentially completely block >> CMA allocations, memory compaction, memory hotunplug, memory poisoning... ?! >> >> That sounds very bad. > > The page under writeback are already unmovable while they are under > writeback. This patch is only making potentially unrelated tasks to > synchronously wait on writeback completion for such pages which in worst > case can be indefinite. This actually is solving an isolation issue on a > multi-tenant machine. > Are you sure, because I read in the cover letter: "In the current FUSE writeback design (see commit 3be5a52b30aa ("fuse: support writable mmap"))), a temp page is allocated for every dirty page to be written back, the contents of the dirty page are copied over to the temp page, and the temp page gets handed to the server to write back. This is done so that writeback may be immediately cleared on the dirty page," Which to me means that they are immediately movable again? -- Cheers, David / dhildenb