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Howlett" , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , David Hildenbrand , Jonathan Corbet , Michal Hocko , Shuah Khan , Randy Dunlap , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Usama Arif , Kiryl Shutsemau , Nirmoy Das , Dragos Tatulea , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , Andrew Morton References: <20260831075635.2244437-1-noren@nvidia.com> From: Lance Yang In-Reply-To: <20260831075635.2244437-1-noren@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: k9bp5956ppqtusucd9w4pjadoprroppc X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 6BDB1120004 X-Rspam-User: X-HE-Tag: 1788166831-307410 X-HE-Meta: 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 qeVW+7S3 q+wcwUVcfDsFh3at2hS3xOVCzJ1vTEvStpBobNAUlCadZN7aF1oFGROCfAMRBJG8rdOWoq2a+8NFJq8GaqV1gYUAzKiaDuKsYOb12TqnUQ7NUv6p6Ad1NrX3mtIUAREOk5bQ5bz/Z/OW2+p8WALzX/rbOwtDhG2cp5zQDQoQmfYk8ydYaupIl8jLgtLq1+m7Wwd6FnRt3Ag0HxZ0NkJavs27qpWMXHLgiEgmEO/WSdhSpCuQbB0Y5BYochsqIJp1F698n89rKIjEASbIu168D3DccXPK+XgEVZa6cXeRh4YuMY16DQZtwnG1/5jR4feSnac/q Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/8/31 15:56, 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. > With MIGRATE_PCPTYPES equal to 3, the formula accounts for 11 > pageblocks for every eligible populated zone before capping the result > at 5% of low memory. > > This is reasonable when a pageblock is 2 MiB, as on common 4 KiB page > configurations, but scales poorly with larger base page sizes. With > the default arm64 pageblock sizes, the contribution per eligible zone > before the 5% cap 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 > > Consequently, min_free_kbytes can reach excessive and unwanted levels. > > Add an absolute 1 GiB cap to the recommendation, in addition to the > existing percentage cap. This bounds the automatic recommendation to a > sane value on systems with large pageblocks while preserving existing > behavior for typical systems with 2 MiB pageblocks. Sorry, I haven't been following the previous discussion. One nit: why 1 GiB? It feels a bit arbitrary to me ...