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(p200300d82f099c0081732a94640ddd31.dip0.t-ipconnect.de. [2003:d8:2f09:9c00:8173:2a94:640d:dd31]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b9a6ecfafsm79703055e9.21.2025.09.03.09.14.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Sep 2025 09:14:24 -0700 (PDT) Message-ID: <78b9c23d-98ce-4b06-9acf-d36c58777d56@redhat.com> Date: Wed, 3 Sep 2025 18:14:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/9] mm/cma: Allow dynamically creating CMA areas To: Thierry Reding Cc: Frank van der Linden , David Airlie , Simona Vetter , Sumit Semwal , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Benjamin Gaignard , Brian Starkey , John Stultz , "T.J. Mercier" , Andrew Morton , Mike Rapoport , dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-tegra@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-mm@kvack.org References: <20250902154630.4032984-1-thierry.reding@gmail.com> <20250902154630.4032984-4-thierry.reding@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 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: Wa0zyfPEkhaUni23TCF5apOwZJqNG8ZFIXXEt_Sep8U_1756916066 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B95C010001D X-Stat-Signature: k6x199jfxq5ji3zkddaymdxt9x99ecj8 X-Rspam-User: X-HE-Tag: 1756916070-483131 X-HE-Meta: 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 ilE5N9pT UhimoyKW9X1FQzi0ztV3BWK8nlVwl04VFA4JwkedXENWy9K9qptBFaodfNLNapqun4E78MLP3uLCcxshhYkLkIcurn6Fj3YxtAkR2ci0Of8buydf421rnarqRzqqqQpYEwNzqbDa+bL71HFeStr3zKJWlnUj1JSB0eZk/iA8q7NvHM4u2uJMVLQY/rPZjAUehOwTx+cbm658s5epAnnV1A0JZ+keaMLVi3CcqdK3jC2GCDnhpI+n2ibnsuBh6TlQFMqQb083oCFfHGsiW6Y5QxD0+kQiNf7H04IiTccErbLNHBtxGoeV4aLexW614Ohc9WuytbAa2ARhw2dkJ4htC6ez8/F0mHDbPjJIUtz8ruwq7MVQ0pZCqwwuOwomq10uXsMHlgOW/57uoJkFJl9uzJW7N5j8MrJ2h+edWrVHRWBSGPCzw87lWPxygg7/MVJ22+AfGeFaZCgcSihjCS9Lkrw94kHz8FAxec8ovnQ9lgJSdWPm3IpJY8BupXTeqUmhjDfqdmf+Nwep4Ren1wcmPhaTc0Mnz7Pjie0qESi0k4bnoYLlIoMkR1JoqDfq3V8W+ybJ5w1QWWVVIHRZyhceXg1StaA== 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 03.09.25 18:12, Thierry Reding wrote: > On Tue, Sep 02, 2025 at 09:04:24PM +0200, David Hildenbrand wrote: >> >>>> +>> +struct cma *__init cma_create(phys_addr_t base, phys_addr_t size, >>>> + unsigned int order_per_bit, const char *name) >>>> +{ >>>> + struct cma *cma; >>>> + int ret; >>>> + >>>> + ret = cma_check_memory(base, size); >>>> + if (ret < 0) >>>> + return ERR_PTR(ret); >>>> + >>>> + cma = kzalloc(sizeof(*cma), GFP_KERNEL); >>>> + if (!cma) >>>> + return ERR_PTR(-ENOMEM); >>>> + >>>> + cma_init_area(cma, name, size, order_per_bit); >>>> + cma->ranges[0].base_pfn = PFN_DOWN(base); >>>> + cma->ranges[0].early_pfn = PFN_DOWN(base); >>>> + cma->ranges[0].count = cma->count; >>>> + cma->nranges = 1; >>>> + >>>> + cma_activate_area(cma); >>>> + >>>> + return cma; >>>> +} >>>> + >>>> +void cma_free(struct cma *cma) >>>> +{ >>>> + kfree(cma); >>>> +} >>>> -- >>>> 2.50.0 >>> >>> >>> I agree that supporting dynamic CMA areas would be good. However, by >>> doing it like this, these CMA areas are invisible to the rest of the >>> system. E.g. cma_for_each_area() does not know about them. It seems a >>> bit inconsistent that there will now be some areas that are globally >>> known, and some that are not. >> >> Yeah, I'm not a fan of that. >> >> What is the big problem we are trying to solve here? Why do they have to be >> dynamic, why do they even have to support freeing? > > Freeing isn't necessarily something that I've needed. It just seemed > like there wasn't really a good reason not to support it. The current > implementation here is not sufficient, though, because we'd need to > properly undo everything that cma_activate_area() does. I think the > cleanup: block in cma_activate_area() is probably sufficient. > > The problem that I'm trying to solve is that currently, depending on the > use-case the kernel configuration needs to be changed and the kernel > rebuilt in order to support it. However there doesn't seem to be a good > technical reason for that limitation. The only reason it is this way > seems to be that, well, it's always been this way. Right, and we can just dynamically grow the array, keep them in a list etc. -- Cheers David / dhildenb