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b=Y+Vq/+knyZI4VnnF4ShT+GGtlQMb3D2bGKxc8fSm27jU7wVLLsruEkfmsGoGukU3A pr9bNxaDsYx8Q61wwldFLMUV2owW66wuz1pa9C4YmtwNof4Etd1KvZO2HxObq7iufu gnYr2+cXjig7nuPPG97J6Xtvfw5YoEAMsggfdeI10fMJ3tMtbvt0Gme3zGHU2vNTnU XlxWGAP0M/mJPqtrExlAnkeczmER+kz8VuKgTh6V9CaBX8LdjYhTDinBnO19+mzXi+ /omcduC71RkDXFwzkYhs7+KBCwuDmOVvO9ulPNEQ2XHQ9eENh+pKB7NWlY4VCe7c5y YMlm2U2X4nFaQ== Message-ID: Date: Tue, 12 May 2026 08:47:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: "alloc_tag was not set" when running mm/ksft_hmm.sh To: Alistair Popple , Zenghui Yu Cc: Zenghui Yu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, jgg@ziepe.ca, leon@kernel.org, Andrew Morton , ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com References: <10e4565a-b416-45d9-a8b0-cd32532b2630@kernel.org> <2b46241c-158b-c9dd-9b81-a98366b2c9fb@huawei.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 0CC3740005 X-Stat-Signature: eh7jqppwidsyk1kueu1hfhskthqzwmxq X-HE-Tag: 1778568474-669554 X-HE-Meta: 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 QISBmGBa l928rbLgPaMalUZ2AQldGtpDMd95ZJOEQtK9SKz5Vk74gB99NjHGguR5bd+DXX0ztoRJcABp5Sx2Cn9aDtQNqQIy+rLEVwBKrghdEapgiWUuAkObsjLx/Fn8OeynHm3Hn8bBo16JrcMBWTrgQrp2ilnIjWpRXpMqkU8QqYFmLqWpaCU0iUBZuyzR1SyneMrEv2GPQKqXD33h2C4SbwlOqNOzAEw7Re4iovB80S3VxMm7XdKE8OFXftiA4xlBap0al2Klyw/TJhckMVAiyqIEAKir3zp61WpIZPJhicLwtZFOoPlfpNUV28UHIPg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/12/26 03:28, Alistair Popple wrote: > On 2026-05-12 at 02:38 +1000, Zenghui Yu wrote... >> Hi David, >> >> On 5/11/26 8:47 PM, David Hildenbrand (Arm) wrote: > > Thanks. I have reproduced it now that my fingers are skinnier. > >>> >>> >>> zone_device_private_split_cb(), that ends up calling ->folio_split(). >>> >>> We do have a call to pgalloc_tag_split() in __split_unmapped_folio(), invoked in >>> __folio_freeze_and_split_unmapped() before calling >>> zone_device_private_split_cb() when iterating the folios. >> >> If I read the code correctly, pgalloc_tag_split() in >> __split_unmapped_folio() deals with device private pages' alloc tag. But >> what alloc_tag_sub_check() warns on are real system memory pages (device >> page's backing page), which are allocated by >> dmirror_devmem_alloc_page()/folio_page(). >> >> static void dmirror_devmem_folio_split(struct folio *head, struct folio >> *tail) >> { >> struct page *rpage = BACKING_PAGE(folio_page(head, 0)); >> >> Thanks, >> Zenghui >> >>> The zone_device_private_split_cb(folio, NULL); is then called on the first folio >>> after looping over the other (new) folios. >>> >>> I would assume that __folio_freeze_and_split_unmapped() would already do the >>> right thing? > > Well you know what they say about assumptions :) Although in this case > __folio_freeze_and_split_unmapped() isn't called on the backing page anyway > (it's called to split the ZONE_DEVICE page, not the page simulating device > memory). Now my brain hurts :) > The problem is we're not splitting the tag associated with the backing > page for the simulated memory. > > I came up with the below fix last night, but I suspect it will quite reasonably > get NACKED on the basis of the symbol export so was looking at other solutions. I think there are other problems ... > > The simulated memory should just be used like a bare physical address range. So > there really is no reason for the backing page simulating device memory to be > allocated as a higher order folio. Using the struct page to store some metadata > for the simulated device is convenient though to avoid creating a test-specific > data structure for this. So I am looking at going back to allocating the > simulated backing memory as always order-0 pages in the test which is what it > was prior to the introduction of large device pages, but that was causing a > crash I'm yet to debug. > ... such as doing a folio_page(folio_alloc()), followed by a __free_pages(). Why are we even allocating folios here and manually splitting them? Looking at dmirror_devmem_folio_split(), aren't we using folios here for something that ... is not a folio? Likely we really shouldn't be using folios here ... :) -- Cheers, David