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b=Tsb6Mhn5W7yHRlJBXykDzeOXgNLdHkKpj0ScceVhTJeGMjwpRaTOu/XBHC5j7/ANp dxH0KoykFdSUCnu9PvxPRfj5amBhduE+D+qptUCZFhlAytu2VhMQ8Q5ucxis9Jj7pN b0yWyz5/X1rDdWboculE//6uVUVqoEREQy7plO7Vz8E4wQkdE6iiEAqoeclt17uO29 L4hF0xUH7Z+fU+Je+2ZdOUT+MFGjVL+ol60h7zDbmwx+eoZOOB15rxGXClEBMWkAJp 42XtgqxHF9BJs4mjc15p2ogvnzDJJfd+dY1GemoudCAhZOnkHBJtAGyrDXuqvwKFhD D17DnqiaryqUQ== Message-ID: <8ef6e92d-4cb3-444e-857e-fdbf88c035ea@kernel.org> Date: Tue, 12 May 2026 09:51:05 +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 Cc: Zenghui Yu , 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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: izsjbjcw7pux4b4sbeehrqghrtcjfg5u X-Rspamd-Queue-Id: 51E63140006 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1778572290-182626 X-HE-Meta: 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 ZjigQPDF s+gaH7ybrZXJ0qmtzb+mufTLhb//QUW0FAPy0F0QCDF86bmdx7xJNy2J8tXjE15VDH0mZziuaNTPX2sOGE9cz9o8wUHDteGhmBQxUk1LuthhgKf1DqLnj4fI3Ru7rftMmCnBR+JlF7NEhF3pZjE0kuw4mT8EJEzAa4KWT9s0VVKpkOh5w7PbKQEHkqp+UXjtrflPVx952ccEjh1HSXEuyNk09xQdGt9k/j/b81VptYAcB3mtdIJ8DmHBo6+O2Lx1uNwc6EnrTNO7Z1bSoZRjCOD3Uu8IfGcFxboIwxFgU1dWkqwz0Lt1JjsDKLYKhzDAcTS3xC6um0O8i+hU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/12/26 09:46, Alistair Popple wrote: > On 2026-05-12 at 16:47 +1000, "David Hildenbrand (Arm)" wrote... >> On 5/12/26 03:28, Alistair Popple wrote: >>> On 2026-05-12 at 02:38 +1000, Zenghui Yu wrote... >>> >>> Thanks. I have reproduced it now that my fingers are skinnier. >>> >>> >>> 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 :) > > I have never liked this bit of the HMM selftests. It has always made my brain > hurt. > >>> 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 ... :) > > Exactly my point, just more succinct :) > > I just need to make it work without doing that. Ok, great. You could also allocate a larger buddy page and just split it manually through split_page. split_page will even do the pgalloc_tag_split :) -- Cheers, David