From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Zi Yan <ziy@nvidia.com>, Johannes Weiner <hannes@cmpxchg.org>
Cc: Usama Arif <usama.arif@linux.dev>,
willy@infradead.org, Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org,
riel@surriel.com, Shakeel Butt <shakeel.butt@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>, Barry Song <baohua@kernel.org>,
Dev Jain <dev.jain@arm.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Nico Pache <npache@redhat.com>,
"Liam R . Howlett" <Liam.Howlett@oracle.com>,
Ryan Roberts <ryan.roberts@arm.com>,
Vlastimil Babka <vbabka@suse.cz>,
Lance Yang <lance.yang@linux.dev>,
Frank van der Linden <fvdl@google.com>
Subject: Re: [LSF/MM/BPF TOPIC] Beyond 2MB: Why Terabyte-Scale Machines Need 1GB Transparent Huge Pages
Date: Thu, 19 Feb 2026 18:09:07 +0100 [thread overview]
Message-ID: <43a065a3-dcff-4d6a-8c5a-c68cda7065ee@kernel.org> (raw)
In-Reply-To: <A4DDD3A2-104A-42BD-B174-676012166BEC@nvidia.com>
On 2/19/26 17:52, Zi Yan wrote:
> On 19 Feb 2026, at 11:48, Johannes Weiner wrote:
>
>> On Thu, Feb 19, 2026 at 05:00:19PM +0100, David Hildenbrand (Arm) wrote:
>>>
>>>
>>> There once was this proposal where we would, instead of splitting a THP,
>>> migrate all memory away instead. That means, instead of splitting the 1
>>> GiB THP, you would instead return it to the page allocator where
>>> somebody else could use it.
>>
>> With TLB coalescing, there is benefit in preserving contiguity. If you
>> lop off the last 4k of a 2M-backed range, a split still gives you 511
>> contiguously mapped pfns that can be coalesced.
>
> Which CPU are you referring to? AMD’s PTE coalescing works up to 32KB
> and ARM’s contig PTE supports larger sizes. BTW, do we have PMD level
> ARM contiguous bit support?
Yes. It's used for hugetlb only so far, obviously (np THP > PMD).
--
Cheers,
David
next prev parent reply other threads:[~2026-02-19 17:09 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-19 15:53 Usama Arif
2026-02-19 16:00 ` David Hildenbrand (Arm)
2026-02-19 16:48 ` Johannes Weiner
2026-02-19 16:52 ` Zi Yan
2026-02-19 17:08 ` Johannes Weiner
2026-02-19 17:09 ` David Hildenbrand (Arm)
2026-02-19 17:09 ` David Hildenbrand (Arm) [this message]
2026-02-19 16:49 ` Zi Yan
2026-02-19 17:13 ` Matthew Wilcox
2026-02-19 17:28 ` Zi Yan
2026-02-19 19:02 ` Rik van Riel
2026-02-20 10:00 ` David Hildenbrand (Arm)
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