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Peter Anvin" , Vlastimil Babka , Zi Yan , Dave Hansen , David Hildenbrand , Lorenzo Stoakes , Andrew Morton , "Liam R . Howlett" , Jens Axboe , linux-kernel@vger.kernel.org, linux-mm@kvack.org, willy@infradead.org, x86@kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, hch@lst.de References: <20250612105100.59144-1-p.raghav@samsung.com> <30a3048f-efbe-4999-a051-d48056bafe0b@intel.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: 7bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 7F29E1C000B X-Stat-Signature: xpa3zxcabi7bi4p5ab5zuia3sfucc5b3 X-Rspam-User: X-HE-Tag: 1749764798-772094 X-HE-Meta: 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 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 6/12/25 13:36, Pankaj Raghav (Samsung) wrote: > On Thu, Jun 12, 2025 at 06:50:07AM -0700, Dave Hansen wrote: >> On 6/12/25 03:50, Pankaj Raghav wrote: >>> But to use huge_zero_folio, we need to pass a mm struct and the >>> put_folio needs to be called in the destructor. This makes sense for >>> systems that have memory constraints but for bigger servers, it does not >>> matter if the PMD size is reasonable (like in x86). >> >> So, what's the problem with calling a destructor? >> >> In your last patch, surely bio_add_folio() can put the page/folio when >> it's done. Is the real problem that you don't want to call zero page >> specific code at bio teardown? > > Yeah, it feels like a lot of code on the caller just to use a zero page. > It would be nice just to have a call similar to ZERO_PAGE() in these > subsystems where we can have guarantee of getting huge zero page. > > Apart from that, these are the following problems if we use > mm_get_huge_zero_folio() at the moment: > > - We might end up allocating 512MB PMD on ARM systems with 64k base page > size, which is undesirable. With the patch series posted, we will only > enable the static huge page for sane architectures and page sizes. Does *anybody* want the 512MB huge zero page? Maybe it should be an opt-in at runtime or something. > - In the current implementation we always call mm_put_huge_zero_folio() > in __mmput()[1]. I am not sure if model will work for all subsystems. For > example bio completions can be async, i.e, we might need a reference > to the zero page even if the process is no longer alive. The mm is a nice convenient place to stick an mm but there are other ways to keep an efficient refcount around. For instance, you could just bump a per-cpu refcount and then have the shrinker sum up all the refcounts to see if there are any outstanding on the system as a whole. I understand that the current refcounts are tied to an mm, but you could either replace the mm-specific ones or add something in parallel for when there's no mm.