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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?fkiQ9cjg2vAkofKwllJrdsWSPcIPF8HcIg6DI5v2Rgq7Jdq+TR0UGl1muksy?= =?us-ascii?Q?VaY/G0OIWbhOx+33A8Ma94CtlSq1rwtqU29WbgNR/r8tWKX66XCoAG13qi0y?= =?us-ascii?Q?XXUB9Y61D0i+k4/72c8sagT0qz1ZButmZwoMTdt8B7IlMSpRhFOPkP5e84Ta?= =?us-ascii?Q?1owicGNuEY7bRDjGtwhnGee34ozOxwDGdc+SgazXWYixUDAGdu1U6Plm7hVi?= =?us-ascii?Q?7du8983gP90ityJXL13xjCTvZgYdUxbludF3DisSaAmrWV57Z2vZReOAvzdc?= =?us-ascii?Q?DzGFAjV35dMYj2jlegtmTJTphpXaV2lH30mjpswHrwTu6ULhFC6FoGKCaAIS?= =?us-ascii?Q?z4WR7xoT/7XFEV18GAxOGMwrxYSnJMpVztx+98MravSqJwj3NkGosRxndNuA?= =?us-ascii?Q?ZhFLmEoEGAmeSNTih5JadUhloM4dOBLlJMLFluDhPy766/N8gA/UHC3Li1pw?= =?us-ascii?Q?Q2DXNW6AFeAv6NWPLnPQJFWU1w/412w4ebw2Z5cP/O1flQLbkXx63cpWA2IM?= =?us-ascii?Q?trRW4cVN6gwvHXJv9cnpdqfWTs0BOdXBbl2E+KW1dQNIm9va+FF/E0YopVan?= =?us-ascii?Q?IkKMEliZHOHsftPQKmdInClM+TYN5CBxPQaiOJTfaulrbIHKZHDLZukkeE0x?= =?us-ascii?Q?J1ksYR8jt9e0Afj1W2si+aRKymQ4eq/ejvPl+EQ8xZjDA0r01/NwPPRcyccQ?= =?us-ascii?Q?tnldCvVPXMT8SV61TzFBC1xj0Da5vy4eaDLFgYPd18Q+nicJftTJZ/OoRnHK?= =?us-ascii?Q?Psbh9l81Ck8mWHUAtFQUGaN+fsQy52bRomtKE3IPIfnO22/gG5xap1YmEq66?= =?us-ascii?Q?CGP9iSfqGRYibNOGi3l59IEubdrh+7+qsny1sUqBnadQf4DWJESpxkezBp+S?= =?us-ascii?Q?3IzH8SXDP26oUMSF1QGQrWGvIqVpv+2JH+vWEl/96aw+hhOV+TsASbpyYwlb?= =?us-ascii?Q?4oyz53JANWNlWioF0SLbAYnjx1bKitufrVR2LCoCFWUtshhEyItTRHWKnq07?= =?us-ascii?Q?dZ+P7IFrpruzkeKolvh9+654EBPALWo6Mz+F4ZA2TY43Vdc+glasvOJbeIfv?= =?us-ascii?Q?xBzbVQ4dJZyUlqtm4fxpEsNPRpHVCI9Y5JhlUy5zd9f/VA0y1XhKpHBXuWuu?= =?us-ascii?Q?/PK9cll47FsJPplIp8xBJvxSYA3VNvGTSesBIvoGLXurqSyQWt19UdRe8zRy?= =?us-ascii?Q?xZ7d9kBc0hiX7DHBYqVf89dfyUxY0wzJhRixnd48QlhQM36DygpTcb371RCo?= =?us-ascii?Q?YvIt21SpmaZXQ7mQd883c4mVCCa9QFkX3wyb8XQwPIwmRLVUndJSabtGMj6Q?= =?us-ascii?Q?IEf7Scw5X/BpM7G46OidTcPinHrB1K3klAMvJRZYUbndjG5ShIVLDjUZ7uYP?= =?us-ascii?Q?gejuR4uhvAZmNHH2+982YLm/ZdDPtFZmDtB+V0JDUY3ep5KsE2HYSXa/HQRf?= =?us-ascii?Q?T1zKOE8N6S/bu5TJUyhrZUjzzs2AVpWxslN/DJP5HkKet/b9ecMMiQ8AOZfF?= =?us-ascii?Q?Jz11igkfKWY0hEXERRTFVSinKNEZvc8GDzciSaAhfLaNjICPd1xAjdZGvURi?= =?us-ascii?Q?CPkQ2yKAKWegxW0BNLJp8NNpSap+K3h29Znn7pQf5xXOnKqxHVVgkwijXowM?= =?us-ascii?Q?xgeXye+IFc2KVi+tTK0j+lNZhFcKIe7dT9M5iBYOIRdLQ8s2n61ABrL6kRxX?= =?us-ascii?Q?hspA4ylwUASbzooTYXbHQstOBJoRcD6JQFHu7t3q/RJp9syEZWpCxJ907rtL?= =?us-ascii?Q?TQ9yrbcCPw=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: df215ffc-3ff8-47d5-2e0d-08df086d5e5c X-MS-Exchange-CrossTenant-AuthSource: IA0PR12MB8374.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Sep 2026 21:09:53.9122 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: P7cEqQYa7Duh5n+xq5WQpbHxDgue6DHAXoPjaPGKOPDMK3n+nxsnPZwlF6ULvcGy X-MS-Exchange-Transport-CrossTenantHeadersStamped: SAWPR12MB999293 On 1 Sep 2026, at 16:44, Johannes Weiner wrote: > On Tue, Sep 01, 2026 at 10:01:23PM +0300, Nimrod Oren wrote: >> When THP is enabled, set_recommended_min_free_kbytes() may raise >> min_free_kbytes using a heuristic that scales with pageblock_nr_pages. >> Commit f000565adb77 ("thp: set recommended min free kbytes") added this >> heuristic to help keep pageblocks free and reduce fragmentation for THP >> allocations. > > We've had problems with compaction before when min_free_kbytes was too > small on large machines. Competing free space scanners do a lot of > work only to fight over a very small set of possible target pages. > > So I'm a bit uneasy that you didn't include any benchmark numbers with > this that prove basic functionality on larger hosts isn't regressed. > >> The recommendation scales poorly with larger base page sizes. With the >> default arm64 pageblock sizes, the contribution per eligible zone >> before applying the existing cap of 5% of low memory is: >> >> 4 KiB pages: 2 MiB pageblock, 22 MiB per zone >> 16 KiB pages: 32 MiB pageblock, 352 MiB per zone >> 64 KiB pages: 512 MiB pageblock, 5.5 GiB per zone > > I question whether pageblocks need to be 512M on those machines to > begin with. After this patch, you're still asking the page allocator > to optimize grouping such that 512M pages can be allocated at > runtime. Only now you took away part of the mechanism to do so. > > If you're using 512M THPs, I would kind of assume it's on machines > with a memory size where 5.5G for defrag purposes isn't devastating. > > And if you're not, it would make more sense to lower the pageblock > size to the mTHP size you're actually using. And that would fix the > "excessive" min_free_kbytes issue as well. But lowering pageblock size requires a kernel compilation. That means maintaining two sets of kernels for different needs. The ultimate solution is to enable better compaction to generate THPs bigger than a pageblock size, like Rik's super-pageblock proposal. After removing automatic min_free_kbytes boosting, user can still increase it via sysctl to restore the old free memory head room. It is much easier, right? > >> The automatic min_free_kbytes increase predates proactive compaction >> and many subsequent changes to compaction. Given those changes, >> increasing min_free_kbytes for THP by default is no longer clearly >> justified. > > That's pretty handwavy. How would these changes specifically eliminate > the need for compaction scratch space and allocator fallback options > to stave off fragmentation during placement? Extra free memory is still necessary. min_free_kbytes can be adjusted at machine boot time to achieve it, right? Best Regards, Yan, Zi