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Sat, 04 May 2024 11:37:40 -0700 (PDT) Received: from p183 ([46.53.248.240]) by smtp.gmail.com with ESMTPSA id x19-20020a170906135300b00a599e418208sm1566800ejb.9.2024.05.04.11.37.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 04 May 2024 11:37:38 -0700 (PDT) Date: Sat, 4 May 2024 21:37:35 +0300 From: Alexey Dobriyan To: gregkh@linuxfoundation.org Cc: andrii@kernel.org, linux-fsdevel@vger.kernel.org, brauner@kernel.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, gregkh@linuxfoundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/5] fs/procfs: implement efficient VMA querying API for /proc//maps Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Stat-Signature: xtrj176oqn7asfroent1aqxhikk8okqc X-Rspamd-Queue-Id: D93531A0017 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1714847861-972071 X-HE-Meta: U2FsdGVkX1/w2Ll+KoYIwDjVjSKW9X4G3lJ4mN/xB5SMnIhaQHl4wqbvdK5UnzGdv+/CTO6hguJjBoeT4Hln/dfWqVkDRR2XfpxnphtyyqNHha4aJ4yy9TIYW4yGE9Tutdz8ROf/+YZGnbqboX0rgOaNUt0/zdif1vyG6moW+HhsPnV9jjx4OcaIdPfxR3H8e5EzQdbM1EGPe4veFMtMms0zyL8wtETSFkwNTfk3YEOPolq3o8tRo2uFrk5MJhn16wgAGejO4HCeDq1K7epKWqasAVjnn5hGyK6dxulp7rs/heQDy+avZ16GMYGrgjqgE7sERE7B3uPj/bL5/0eRImXsCwP9J9yjXwVqkjmtzputwywJQ8dKdnb+SH5WRkCS5VfXDjbWyMXVtWChVOxAVXiIO1Dx0uPif1BQDvmqjmlhmYnBuPUsBmY1guTOWj/W2Ad74u5xDaFo08dGS0ZCfP6R5WR0lRGVjT9eFdaLyburGw2YBzvFHggvC5CbnsQ/AFkqAlt6YR+m+yiS6vN+LEYZfP35mPnZTKz8L7k58gI0gsr8Zi+dJLAWpA1Hz6dyzsRSY6oii9+9+sMn5I3S3cPESiYOaXvOd03ZRR2XsqMGJPVZG1NdXpw8kGu/gQ7zbVkQIB6uszmmknC2+f//kgIlhQAvmCYUE71BkoeVBTXjLxUvL47vLaAM+dey4w8H3bti+0PEA/Ft9aSUTRmG42JNZzc6BSaTYX3Jp2lKdSJ2TB6QpN8CT2Kq7ZpBLxczsQqvtlkb6Gzi543MOIjw1YGpSO/fKwpiHNysBkuOv8/Zz7T6Wq6IFn8vPI2GxE/iUP+AzmvARVRDXvxrAOlsJAD4OX/pA9IhhMSOCZji9YApHWH5twN5mEdHmOORgbP6np4jEmDb1yHIVcesIDk2HzczJB/Ew8UD+TSMKwKtkBhAp5IjONyDaQPdcg78PphXS4+uYfyglZEVMXXfeeN ZC33HUx0 OgAvF1l0vGBQdGRhVD5QF8Nj9B5jzPLVEaAZQyoDpioA6TSOVUzMuTf//2Av/0XdBoa0KNuJDXrAhZ/4SrmG0z4ast4uJhkAdbrpllZEit7xcxpGMXS+NNr0IpuptIcnEOhtHWaja7WTX7M6Fl/NKwZbhP+yRDiiarpNTR4spR6twmsdXh65eSgvHLrAn0iVvydoGhc8yt6yXgMUiHC1P0Yn6/5pqzw8nvpZrU7yKubdCWHGsV03Froi8WQfhfJOqDqZj0PaTlO4Jbzlpfdf2aVCofjoiCM6buK+WfjsC09YIEUShcoeGcrRNPUhKx5OlN18U6u/X8OSLDcY6Zyiki3CkTLLIAVnAdAWrWH8Qu7kLp117sXwLQ1iMeSFInrPfBPl/CRjcGJZsuah4EvPHjclXqZpEU5ZLjgBV0Piy0CW6VH7RbYEiGN6zt4Y0S+zFFPlAI0OOD2pMNec= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000143, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi, Greg. We've discussed this earlier. Breaking news: /proc is slow, /sys too. Always have been. Each /sys file is kind of fast, but there are so many files that lookups eat all the runtime. /proc files are bigger and thus slower. There is no way to filter information. If someone would post /proc today and said "it is 20-50-100" times slower (which is true) than existing interfraces, linux-kernel would not even laugh at him/her. > slow in what way? open/read/close is slow compared to equivalent not involving file descriptors and textual processing. > Text apis are good as everyone can handle them, Text APIs provoke inefficient software: Any noob can write for name in name_list: with open(f'/sys/kernel/slab/{name}/order') as f: slab_order = int(f.read().split()[0]) See the problem? It's inefficient. No open("/sys", O_DIRECTORY|O_PATH); No openat(sys_fd, "kernel/slab", O_DIRECTORY|O_PATH); No openat(sys_kernel_slab, buf, O_RDONLY); buf is allocated dynamically many times probably, it's Python after all. buf is longer than necessary. pathname buf won't be reused for result. .split() conses a list, only to discard everything but first element. Internally, sysfs allocates 1 page, instead of putting 1 byte somewhere in userspace memory. /proc too. Lookup is done every time (I don't think sysfs caches dentries in dcache but I may be mistaken, so lookup is even slower). Multiply by many times monitoring daemons run this (potentially disturbing other tasks). > ioctls are harder for obvious reasons. What? ioctl are hard now? Text APIs are garbage. If it's some crap in debugfs then noone cares. But /proc/*/maps is not in debugfs. Specifically on /proc/*/maps: * _very_ well written software know that unescaping needs to be done on pathname * (deleted) and (unreachable) junk. readlink and /proc/*/maps don't have space for flags for unambigious deleted/unreachable status which doesn't eat into pathname -- whoops > I don't understand, is this a bug in the current files? If so, why not > just fix that up? open/read DO NOT accept file-specific flags, they are dumb like that. In theory /proc/*/maps _could_ accept pread(fd, buf, sizeof(buf), addr); and return data for VMA containing "addr", but it can't because "addr" is offset in textual file. Such offset is not interesting at all. > And again "efficient" need to be quantified. * roll eyes * > Some people find text easier to handle for programmatic use :) Some people should be barred from writing software by Programming Supreme Court or something like that.