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Wed, 14 Oct 2026 13:32:15 -0700 (PDT) Date: Wed, 14 Oct 2026 22:32:14 +0200 From: Johannes Weiner To: Nimrod Oren Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jonathan Corbet , Shuah Khan , Randy Dunlap , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Brendan Jackman , David Laight , linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: stop recalculating min_free_kbytes once set by userspace Message-ID: <20261014203214.GF371161@cmpxchg.org> References: <20261014140859.1006967-1-noren@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261014140859.1006967-1-noren@nvidia.com> X-Rspamd-Queue-Id: A425540005 X-Rspam-User: X-Rspamd-Server: rspam12 X-Stat-Signature: ei6941zm3ctd7efruxz6wxaau5qimck1 X-HE-Tag: 1792009936-444362 X-HE-Meta: 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 tSdryZfx 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 14, 2026 at 05:08:59PM +0300, Nimrod Oren wrote: > min_free_kbytes is recalculated on memory hotplug and on THP sysfs > writes. The new value comes from calculate_min_free_kbytes() or, while > THP is enabled, from set_recommended_min_free_kbytes(). A value written > to the vm.min_free_kbytes sysctl is replaced whenever the new value is > higher, so a lower value does not stick. This matters most when THP is > enabled on configurations with large pageblocks, where the new value > can be excessive [1]. > > Stop recalculating min_free_kbytes once a value has been written to the > sysctl. Systems where the sysctl is never written keep the current > behavior. > > Link: https://lore.kernel.org/r/20260716173504.760369-1-noren@nvidia.com/ [1] > Suggested-by: Vlastimil Babka (SUSE) > Link: https://lore.kernel.org/r/d202dcc3-d7d7-4e98-a9a5-3137cfbfd041@kernel.org/ > Signed-off-by: Nimrod Oren Reviewed-by: Johannes Weiner