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[2003:cb:c749:6600:b73a:466c:e610:686]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43656b4432dsm55513135e9.41.2024.12.19.08.29.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 08:29:09 -0800 (PST) Message-ID: <43e13556-18a4-4250-b4fe-7ab736ceba7d@redhat.com> Date: Thu, 19 Dec 2024 17:29:08 +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 , Zi Yan 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 , 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: gmU651R6oziVo7hcu2OlCioJukR9Q8JeLIWKyJsa4Pc_1734625751 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 5BF65100007 X-Stat-Signature: gjq1mkxkw5dfxhmnd84njx43gknsa5bq X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1734625718-691045 X-HE-Meta: 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 vQITZz63 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000793, 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 17:22, Shakeel Butt wrote: > On Thu, Dec 19, 2024 at 10:55:10AM -0500, Zi Yan wrote: >> On 19 Dec 2024, at 10:53, Shakeel Butt wrote: >> >>> On Thu, Dec 19, 2024 at 04:47:18PM +0100, David Hildenbrand wrote: >>>> 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? >>> >>> Oh sorry, my mistake, yes this will become an isolation issue with the >>> removal of the temp page in-between which this series is doing. I think >>> the tradeoff is between extra memory plus slow write performance versus >>> temporary unmovable memory. >> >> No, the tradeoff is slow FUSE performance vs whole system slowdown due to >> memory fragmentation. AS_WRITEBACK_INDETERMINATE indicates it is not >> temporary. > > If you check the code just above this patch, this > mapping_writeback_indeterminate() check only happen for pages under > writeback which is a temp state. Anyways, fuse folios should not be > unmovable for their lifetime but only while under writeback which is > same for all fs. But there, writeback is expected to be a temporary thing, not possibly: "AS_WRITEBACK_INDETERMINATE", that is a BIG difference. I'll have to NACK anything that violates ZONE_MOVABLE / ALLOC_CMA guarantees, and unfortunately, it sounds like this is the case here, unless I am missing something important. -- Cheers, David / dhildenb