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(p200300d82f07dd00ca9c199ed2b69099.dip0.t-ipconnect.de. [2003:d8:2f07:dd00:ca9c:199e:d2b6:9099]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3ee0fbfedd6sm2725928f8f.60.2025.09.18.01.50.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Sep 2025 01:50:52 -0700 (PDT) Message-ID: Date: Thu, 18 Sep 2025 10:50:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/vmstat: add header line to /proc/buddyinfo output To: Ye Liu , Michal Hocko Cc: Andrew Morton , Ye Liu , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250918071741.526280-1-ye.liu@linux.dev> <1a9f44a1-855c-450e-9dc4-415a29b90011@linux.dev> <780aa9d6-a85c-4050-820e-c0ca9f5bb658@redhat.com> <6d6e2e33-c221-4ab8-a29b-3d14fb1a592c@linux.dev> From: David Hildenbrand Content-Language: en-US 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: <6d6e2e33-c221-4ab8-a29b-3d14fb1a592c@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 18.09.25 10:31, Ye Liu wrote: > > > 在 2025/9/18 16:16, David Hildenbrand 写道: >> On 18.09.25 10:11, Ye Liu wrote: >>> >>> >>> 在 2025/9/18 15:29, Michal Hocko 写道: >>>> On Thu 18-09-25 15:17:40, Ye Liu wrote: >>>>> From: Ye Liu >>>>> >>>>> Add a header line to /proc/buddyinfo that shows the order numbers >>>>> for better readability and clarity. >>>>> >>>>> Before: >>>>> Node 0, zone      DMA      0      0      0      0      0      0      0 ... >>>>> Node 0, zone    DMA32      5      8      6      6      7      5      8 ... >>>>> Node 0, zone   Normal   1113    351    138     65     38     31     25 ... >>>>> >>>>> After: >>>>> Free pages per order       0      1      2      3      4      5      6 ... >>>>> Node 0, zone      DMA      0      0      0      0      0      0      0 ... >>>>> Node 0, zone    DMA32      5      8      6      6      7      5      8 ... >>>>> Node 0, zone   Normal   1113    351    138     65     38     31     25 ... >>>> >>>> Why is this needed? And have you considered tha this might break >>>> existing parsers of the file? >>>> >>> >>> Thanks for the review. >>> >>> The reason for this change is simply to make /proc/buddyinfo self-describing. >>> Right now you have to know which column is which order; with a header it’s >>> obvious. This is similar to what /proc/pagetypeinfo already does, e.g.: >>> >>>    Page block order: 9 >>>    Pages per block: 512 >>> >>>    Free pages count per migrate type at order   0 1 2 3 ... >>>    Node 0, zone DMA, type Unmovable             0 0 0 ... >>> >>> Regarding existing parsers: the patch does not change any of the existing >>> “Node … zone …” lines, it only adds a single header line before them. Most >>> parsers match “Node” lines and ignore everything else, so the risk should be >>> low. If you know of any existing parser that this would break, please let >>> me know so I can address it. >> >> What if there is a single one out there that has hardcoded to skip the first line only? > > I understand there may be no way to be fully compatible with all existing > parsers. However, /proc/buddyinfo is essentially raw data intended for > human and tool consumption, and parsers are expected to be robust against > format changes. Let's take a look at a random one: pcp-buddyinfo. Reading the source code [1] of the /proc/buddyinfo parser in refresh_proc_buddyinfo() I have my doubts: if ((fp = linux_statsfile("/proc/buddyinfo", buf, sizeof(buf))) == NULL) return -oserror(); while (fgets(buf,sizeof(buf),fp) != NULL) { char node_name[128]; char *zone_name; unsigned int values[SPLIT_MAX]; i = read_node_name(buf, node_name); i+=6; /* erase ", zone" */ read_buddyinfo(buf+i, read_buf, MAX_ORDER+1); /* read zone name and page order */ zone_name=read_buf[0]; for (i=0; i < MAX_ORDER; i++) values[i] = strtoul(read_buf[i+1], NULL, 10); for (i=0; i < proc_buddyinfo->nbuddys; i++) { if (strcmp(proc_buddyinfo->buddys[i].node_name, node_name)==0 && strcmp(proc_buddyinfo->buddys[i].zone_name, zone_name)==0) break; } Do you think that one would survive your changes? https://github.com/performancecopilot/pcp/blob/main/src/pmdas/linux/proc_buddyinfo.c -- Cheers David / dhildenb