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Howlett" , Mike Rapoport , Matthew Wilcox , Johannes Weiner , Usama Arif References: Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9A16B14000F X-Stat-Signature: ootdqkfnc8p31je4czgj8zyhjaxajry8 X-HE-Tag: 1771520939-627431 X-HE-Meta: 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 fJIDHSQw OdESWH7/1AYr3W3FxxXcI2+YT+DP8w2iCabrHLyF2dvl2ARDjJwS91Wn/vJB9stzaAyS14bI0szBkri8Fz3ukyK4/VL1swYQh+nERFqTKShLq9MrKcQFtUSUt2vl5zAbA6FNfGiUj9LEpt54MQriOOUD4KIZB9zU1qPBWgqhL413PNYPjDit5l5eZ2fP10TksonGfm0gRHgeXfQw= 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 2/19/26 07:08, Kiryl Shutsemau wrote: > - The order-0 page size cuts struct page overhead by a factor of 16. From > ~1.6% of RAM to ~0.1%; First of all, this looks like fun. Nice work! I'm not opposed at all in concept to cleaning up things and doing the logical separation you described to split buddy granularity and mapping granularity. That seems like a worthy endeavor and some of the union/#define tricks look like a likely viable way to do it incrementally. But I don't think there's going to be a lot of memory savings in the end. Maybe this would bring the mem= hyperscalers back into the fold and have them actually start using 'struct page' again for their VM memory. Dunno. But, let's look at my kernel directory and round the file sizes up to 4k, 16k and 64k: find . -printf '%s\n' | while read size; do echo \ $(((size + 0x0fff) & 0xfffff000)) \ $(((size + 0x3fff) & 0xffffc000)) \ $(((size + 0xffff) & 0xffff0000)); done ... and add them all up: 11,297,648 KB - on disk 11,297,712 KB - in a 4k page cache 12,223,488 KB - in a 16k page cache 16,623,296 KB - in a 64k page cache So a 64k page cache eats ~5GB of extra memory for a kernel tree (well, _my_ kernel tree). In other words, if you are looking for memory savings on my laptop, you'll need ~300GB of RAM before 'struct page' overhead overwhelms the page cache bloat from a single kernel tree. The whole kernel obviously isn't in the page cache all at the same time. The page cache across the system is also obviously different than a kernel tree, but you get the point. That's not to diminish how useful something like this might be, especially for folks that are sensitive to 'struct page' overhead or allocator performance. But, it will mostly be getting better performance at the _cost_ of consuming more RAM, not saving RAM.