From: Andrew Morton <akpm@linux-foundation.org>
To: Nimrod Oren <noren@nvidia.com>
Cc: David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
"Liam R. Howlett" <liam@infradead.org>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>, Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>, Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Nico Pache <nico.pache@linux.dev>,
"Ryan Roberts" <ryan.roberts@arm.com>,
Dev Jain <dev.jain@arm.com>, Barry Song <baohua@kernel.org>,
Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>,
Brendan Jackman <brendan.jackman@linux.dev>,
Johannes Weiner <hannes@cmpxchg.org>,
"David Laight" <david.laight.linux@gmail.com>,
<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
Date: Wed, 14 Oct 2026 14:48:23 -0700 [thread overview]
Message-ID: <20261014144823.8c89da26c547fa95936a2fe5@linux-foundation.org> (raw)
In-Reply-To: <20261014140859.1006967-1-noren@nvidia.com>
On Wed, 14 Oct 2026 17:08:59 +0300 Nimrod Oren <noren@nvidia.com> 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.
This problem lies somewhere in the range of "minor annoyance" to
"catastrophically horrible", but it isn't clear where in that range it
falls.
So can we please can we have a paragraph which explains the real-world
userspace-visible runtime effects of this problem?
prev parent reply other threads:[~2026-10-14 21:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-14 14:08 Nimrod Oren
2026-10-14 20:32 ` Johannes Weiner
2026-10-14 20:34 ` Zi Yan
2026-10-14 21:48 ` Andrew Morton [this message]
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