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[2003:cb:c708:7900:b88e:c72a:abbd:d3d9]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-432b05c0d33sm27963635e9.27.2024.11.07.07.07.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Nov 2024 07:07:09 -0800 (PST) Message-ID: <4febc035-a4ff-4afe-a9a0-d127826852a9@redhat.com> Date: Thu, 7 Nov 2024 16:07:08 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: David Hildenbrand Subject: [ISSUE] split_folio() and dirty IOMAP folios 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 To: linux-fsdevel@vger.kernel.org, "linux-mm@kvack.org" , kvm@vger.kernel.org Cc: Zi Yan , Matthew Wilcox , Christian Brauner , "Darrick J. Wong" , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Thomas Huth X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: FzsEWbW7b8ARx_I5wW7TO0PPL6DIA18ZX-quHftDDTE_1730992031 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: rspam06 X-Rspamd-Queue-Id: 4484CC0024 X-Stat-Signature: xx541sq86aygzubaijy496zj1szq88pz X-Rspam-User: X-HE-Tag: 1730992018-317786 X-HE-Meta: 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 MkELLKW5 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.017470, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, I'm debugging an interesting problem: split_folio() will fail on dirty folios on XFS, and I am not sure who will trigger the writeback in a timely manner so code relying on the split to work at some point (in sane setups where page pinning is not applicable) can make progress. https://issues.redhat.com/browse/RHEL-58218 s390x PV ("Protected Virtualization" / "Secure virtualization") does not support large folios. So when we want to convert an individual 4k page to "secure" and we hit a large folio, we have to split it. In gmap_make_secure(), we call split_folio() if we hit a large folio, and essentially retry forever (after dropping the folio reference). Starting a "protected VM" (similar to encrypted VMs) will not make progress when trying to load the initial encrypted VM state into memory ("unpack"). I assume other split_folio() users might similarly be affected: split_folio() will frequently just fail without any obvious way to "fix that up" to make progress. Looking into the details, it seems to be an IOMAP limitation: split_folio() will keep failing in filemap_release_folio() because iomap_release_folio() fails on dirty folios. I would have expected background writeback to "fix that", but it's either not happening or because it's just happening too slowly. I can see that migration code manually triggers writeback, using folio_clear_dirty_for_io() and mapping->a_ops->writepages) when it stumbles over a dirty folio. Should we do the same in split_folio() directly? Or offer callers (gmap_make_secure()) a way to trigger this conditionally, similarly to how we have ways for waiting for a folio that is under writeback to finish? ... or is there a feasible way forward to make iomap_release_folio() not bail out on dirty folios? The comment there says: "If the folio is dirty, we refuse to release our metadata because it may be partially dirty. Once we track per-block dirty state, we can release the metadata if every block is dirty." -- Cheers, David / dhildenb