From: Zi Yan <ziy@nvidia.com>
To: Lance Yang <lance.yang@linux.dev>
Cc: Nimrod Oren <noren@nvidia.com>,
"Liam R. Howlett" <liam@infradead.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Vlastimil Babka <vbabka@kernel.org>,
David Hildenbrand <david@kernel.org>,
Jonathan Corbet <corbet@lwn.net>, Michal Hocko <mhocko@suse.com>,
Shuah Khan <skhan@linuxfoundation.org>,
Randy Dunlap <rdunlap@infradead.org>,
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>, Usama Arif <usama.arif@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>, Nirmoy Das <nirmoyd@nvidia.com>,
Dragos Tatulea <dtatulea@nvidia.com>,
linux-mm@kvack.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, Lorenzo Stoakes <ljs@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v2] mm/khugepaged: cap min_free_kbytes recommendation at 1 GiB
Date: Mon, 31 Aug 2026 11:01:16 -0400 [thread overview]
Message-ID: <28FC994B-F63D-493A-B86E-F87E37B303B1@nvidia.com> (raw)
In-Reply-To: <8411e51c-92fe-41b0-9de0-e9cfc5a50301@linux.dev>
On 31 Aug 2026, at 5:00, Lance Yang wrote:
> 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 ...
It is. Just better than 5.5GiB in the existing configuration.
Best Regards,
Yan, Zi
next prev parent reply other threads:[~2026-08-31 15:01 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-31 7:56 [PATCH v2] mm/khugepaged: cap min_free_kbytes recommendation at 1 GiB Nimrod Oren
2026-08-31 8:47 ` Kiryl Shutsemau
2026-08-31 8:57 ` Lorenzo Stoakes (ARM)
2026-08-31 9:00 ` Lorenzo Stoakes (ARM)
2026-08-31 9:00 ` Lance Yang
2026-08-31 15:01 ` Zi Yan [this message]
2026-08-31 9:20 ` Michal Hocko
2026-08-31 9:34 ` Lorenzo Stoakes (ARM)
2026-08-31 15:00 ` Zi Yan
2026-08-31 15:59 ` Lorenzo Stoakes (ARM)
2026-08-31 17:08 ` Nimrod Oren
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