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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee07407ccasm27885367f8f.15.2025.09.24.05.19.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 05:19:38 -0700 (PDT) Message-ID: Date: Wed, 24 Sep 2025 14:19:37 +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 Cc: Zi Yan , 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> <81a827ce-24f7-4038-bca7-c96dc558cb38@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 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: JKXeaXLNDZtGvl9dcH-8B8BeAZ9Y3vTk2SmWOwke__Q_1758716380 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D22C4180008 X-Stat-Signature: m4wxr64xictw4s5q1n36ybms8em93au1 X-HE-Tag: 1758716382-567283 X-HE-Meta: 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 IG/e/B7r J0tpxEw7Lh7obXXpJQhjqd0LJAZG56MsxQyZHuxcY/zjY0lJSGA78lGbVYqbp4cHWhf/1iyeJiZRXqo7xT8S+NaK0zQIQdvcvXQoMs6++8+7C4XJoPM09iNRVNKiWzsOb58HMmz5wO3VP4YurjjCT4K+9g9ZpALYjiigy 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 14:01, Michal Hocko wrote: > On Wed 24-09-25 13:40:58, David Hildenbrand wrote: >> 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. > > I thought we have concluded that there is no user expecting a specific > alignment. Or have I misunderstood that? We concluded that for users that don't pass in non-power-2 requests. hugetlb->folio_alloc_gigantic()->alloc_contig_pages_noprof() certainly expects a suitable alignment :) I'll note that if no alignment is required, the whole loop in alloc_contig_pages_noprof() is not optimal, because we could be skipping suitable ranges. But I guess nobody cares about that right now -- and at least it's simple. -- Cheers David / dhildenb