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Peter Anvin" , Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook , linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260424191456.2679717-1-stevensd@google.com> From: Dave Hansen Content-Language: en-US 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: 8bit X-Rspam-User: X-Rspamd-Queue-Id: BD89D80006 X-Rspamd-Server: rspam04 X-Stat-Signature: awdmyihgoodzkd3dogz8z8uk78f9gzuf X-HE-Tag: 1777069292-774017 X-HE-Meta: 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 9NEl2Qze yrAZxcA9fjUUrJpAimnjMQZge1N8ZZ8Zm9OGzueStZQHpnaA0d8S1gMXj6+1Wf22pE400N4fFs8nOQILfKGJ6qn2o71kKn7aVIrFGTYP12xIWkeIKj9uKWu468pGsGntJJ4ugQosWFHGZNXm6AjXFI1OscP+UYkXeIxlkEAccbw9RKFebfNjbK5WMMNF2tanGRgmOFd+NA8bWcN2gCsUmfO761rSpN2WWvpTE Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/24/26 14:35, Pasha Tatashin wrote: > On 04-24 12:41, Dave Hansen wrote: >> On 4/24/26 12:14, David Stevens wrote: >>> The question is then: is this approach something that is fundamentally >>> untenable in the kernel >> Yes. Fundamentally untenable. >> >> Not allowing stack faults has been a wonderful simplification. It's one >> of those things that just plain makes the kernel easier to maintain. >> Saving low single digits of system memory is not exactly making me eager >> to go back to the harder-to-maintain days. >> >> I seriously doubt that this 1% is the lowest hanging fruit for memory >> bloat on these systems. 😉 > This true until, in a fleet of millions of machines, you encounter a > one-in-a-billion chance of a stack overflow. You are then forced to > double the statically allocated kernel stacks on every machine, paying a > memory tax even though 99.999..% of threads never exceed 4K. This > overhead accumulates to petabytes of wasted capacity. I don't disagree with you. But, at that point, you're picking your poison: bugs dynamic kernel stacks versus crashes from stack overflows. At some point, I might be able to be talked into dynamic stack as a FRED-only feature. But FRED isn't widespread enough to go to the trouble today. I'm sure the folks who want this also don't want to wait until all the devices in the field have FRED because that even *longer* off. So maybe this is one of those things that folks just need to deploy out-of-tree for a couple of years, come back with some data to show us that we were just paranoid, and we'll look at it again.