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[2003:cb:c719:1700:56dc:6a88:b509:d3f3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a1c828f8fsm49103562f8f.12.2025.01.07.00.34.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Jan 2025 00:34:56 -0800 (PST) Message-ID: <791d4056-cac1-4477-a8e3-3a2392ed34db@redhat.com> Date: Tue, 7 Jan 2025 09:34:49 +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 , Miklos Szeredi Cc: Joanne Koong , Bernd Schubert , Zi Yan , linux-fsdevel@vger.kernel.org, jefflexu@linux.alibaba.com, josef@toxicpanda.com, linux-mm@kvack.org, kernel-team@meta.com, Matthew Wilcox , Oscar Salvador , Michal Hocko References: <0ed5241e-10af-43ee-baaf-87a5b4dc9694@redhat.com> <446704ab-434e-45ac-a062-45fef78815e4@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: e-WlH-q2wbPLFpc8biDI50izJHNORhjuGiZu8bj5ExE_1736238898 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: rspam04 X-Rspamd-Queue-Id: 23D15120005 X-Stat-Signature: 3wnushicdtwhdszpuzx4n1dfxjtfru17 X-Rspam-User: X-HE-Tag: 1736238902-935995 X-HE-Meta: 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 HCmILhZd tluk+SGPvoDlVe6c/11HkRAGmVFyAqCjLQQTKMTusX9Tx42dBeGFwcxAu1sXjsh1XCwm4rYN+G8bheCXhBOCSgKzh6p6TauSUYZEBGvTSX5FuIst0zf0Jx9R6TT2DwCUP+DQWUsKfN19cZnzvSuEcP5yhSdHrR0vDXI81+dTzUi3k/YshBlSKLgKn17gUmKIpkwbG4QrXGTU3DYMHm/Tnz4Eo9v+uefSVhFZDaZ9iLcMgL/AT7OVcMP4SY8sQFjKQvDJba94fKKDIT3AdVyfSt6YZ/1Kxu/2iUpJQa7vZlFKbxA1kVPV8VZSR1tJ0KcVGdoph0RCHUpW5T++xaGhOlo0zJJe9ta9Ltaus01rtObyjJWhz59P6vWXqhpH+04y8BvjwGcU6QWFCxMfbc2tnFCYNlNDkl/ck1ttApHOPJBdDHUTrmPBwqhj28XdX0qB5oMRVUmRu4/scycyymC517/UKiw== 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 06.01.25 19:17, Shakeel Butt wrote: > On Mon, Jan 06, 2025 at 11:19:42AM +0100, Miklos Szeredi wrote: >> On Fri, 3 Jan 2025 at 21:31, David Hildenbrand wrote: >>> In any case, having movable pages be turned unmovable due to persistent >>> writaback is something that must be fixed, not worked around. Likely a >>> good topic for LSF/MM. >> >> Yes, this seems a good cross fs-mm topic. >> >> So the issue discussed here is that movable pages used for fuse >> page-cache cause a problems when memory needs to be compacted. The >> problem is either that >> >> - the page is skipped, leaving the physical memory block unmovable >> >> - the compaction is blocked for an unbounded time >> >> While the new AS_WRITEBACK_INDETERMINATE could potentially make things >> worse, the same thing happens on readahead, since the new page can be >> locked for an indeterminate amount of time, which can also block >> compaction, right? Yes, as memory hotplug + virtio-mem maintainer my bigger concern is these pages residing in ZONE_MOVABLE / MIGRATE_CMA areas where there *must not be unmovable pages ever*. Not triggered by an untrusted source, not triggered by an trusted source. It's a violation of core-mm principles. Even if we have a timeout of 60s, making things like alloc_contig_page() wait for that long on writeback is broken and needs to be fixed. And the fix is not to skip these pages, that's a workaround. I'm hoping I can find an easy way to trigger this also with NFS. > > Yes locked pages are unmovable. How much of these locked pages/folios > can be caused by untrusted fuse server? > >> >> What about explicitly opting fuse cache pages out of compaction by >> allocating them form ZONE_UNMOVABLE? > > This can be done but it will change the memory condition of the > users/workloads/systems where page cache is the majority of the memory > (i.e. majority of memory will be unmovable) and when such systems are > overcommitted, weird corner cases will arise (failing high order > allocations, long term fragmentation etc). In addition the memory > behind CXL will become unusable for fuse folios. Yes. > > IMHO the transient unmovable state of fuse folios due to writeback is > not an issue if we can show that untrusted fuse server can not cause > unlimited folios under writeback for arbitrary long time. See above, I disagree. -- Cheers, David / dhildenb