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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3f02f332c31sm21831543f8f.45.2025.09.24.04.40.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 04:40:59 -0700 (PDT) Message-ID: <81a827ce-24f7-4038-bca7-c96dc558cb38@redhat.com> Date: Wed, 24 Sep 2025 13:40:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/page_alloc: fix alignment for alloc_contig_pages_noprof() To: Michal Hocko , Zi Yan Cc: Anshuman Khandual , Dev Jain , Wei Yang , akpm@linux-foundation.org, vbabka@suse.cz, surenb@google.com, jackmanb@google.com, hannes@cmpxchg.org, linux-mm@kvack.org, Oscar Salvador References: <20250923001943.2479-1-richard.weiyang@gmail.com> <3BF1389C-4B8E-4F50-AB0B-F0D96833D387@nvidia.com> <5491dfda-862a-4c31-b64f-5339007a5302@arm.com> <09284390-5a1a-47e0-9929-0a5ba98c836e@redhat.com> <760C8EBD-9201-4680-8B9B-CAD7641A81C4@nvidia.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: bszth41LFuYqbQKero_FnShLfgB7UamBVZ6V32MTl8M_1758714061 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: 323CF4000D X-Stat-Signature: wwgetfswpp86cq7p8n7h6pcuxrpxw63j X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1758714066-327522 X-HE-Meta: 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 Xclqynfq 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 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 24.09.25 13:32, Michal Hocko wrote: > On Tue 23-09-25 11:07:28, Zi Yan wrote: >> On 23 Sep 2025, at 3:48, David Hildenbrand wrote: >> >>> On 23.09.25 09:06, Anshuman Khandual wrote: >>>> On 23/09/25 7:16 AM, Zi Yan wrote: >>>>> On 22 Sep 2025, at 20:19, Wei Yang wrote: >>>>> >>>>>> Commit 5e27a2df03b8 ("mm/page_alloc: add alloc_contig_pages()") >>>>>> introduced generic method for alloc_contig_pages(). But the alignment >>>>>> calculation seems wrong. >>>>>> >>>>>> Since ALIGN() only accept power of two value, while nr_pages could be >>>>>> any positive one, the result is not defined. >>>>> >>>>> The result would not be any value lower than zone->zone_start_pfn, >>>>> so the worst case is getting an unaligned PFN range. I guess >>>>> most of the time nr_pages would be power of 2. >>>> >>>> Agreed. >>>> >>>> Also as Dev had pointed out earlier, this function gives no >>>> guarantee on alignment of non-power-of-2 requests. Hence I >>>> don't have a strong opinion either way, but does it really >>>> qualify for a "Fixes:" tag ? >>> >>> I'd say if there is nothing to fix, then this patch is not required. >>> >>> What likely does make sense would be that a non-power-of-2 would be aligned to the smallest contained power of 2. >>> >>> E.g., a 6 MiB request would be aligned to 2 MiB instead of multiples of 6 MiB. >>> >>> Not sure what the existing ALIGN would do with that ... >> >> Something like the code below: >> >> pfn = ALIGN(zone->zone_start_pfn, rounddown_pow_of_two(nr_pages)); > > Please let's not try to fix a non-existent problem here. If there is no > alignement requirement then make sure we document it and drop the > existing ALIGN which doesn't seem to serve any actual purpose rather > than make the code more subtle and more obscure for no known reason. I think we need at least one initial align because the zone_start_pfn might not be aligned to the desired order/nr_pages. So I don't think we can drop it. -- Cheers David / dhildenb