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Howlett" , Nico Pache , Dev Jain , Barry Song , Jonathan Corbet , linux-kernel@vger.kernel.org, Shuah Khan , Usama Arif , Andi Kleen References: <20260304155636.77433-1-david@kernel.org> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Lance Yang In-Reply-To: <20260304155636.77433-1-david@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 8C5631C0013 X-Stat-Signature: 9996nmfet6hmwiwooy1x4tb87s69nomo X-Rspam-User: X-HE-Tag: 1772680927-829833 X-HE-Meta: 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 uV6fs0Yz 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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 2026/3/4 23:56, David Hildenbrand (Arm) wrote: > There was recently some confusion around THPs and the interaction with > KernelPageSize / MMUPageSize. Historically, these entries always > correspond to the smallest size we could encounter, not any current > usage of transparent huge pages or larger sizes used by the MMU. > > Ever since we added THP support many, many years ago, these entries > would keep reporting the smallest (fallback) granularity in a VMA. > > For this reason, they default to PAGE_SIZE for all VMAs except for > VMAs where we have the guarantee that the system and the MMU will > always use larger page sizes. hugetlb, for example, exposes a custom > vm_ops->pagesize callback to handle that. Similarly, dax/device > exposes a custom vm_ops->pagesize callback and provides similar > guarantees. > > Let's clarify the historical meaning of KernelPageSize / MMUPageSize, > and point at "AnonHugePages", "ShmemPmdMapped" and "FilePmdMapped" > regarding PMD entries. > > While at it, document "FilePmdMapped", clarify what the "AnonHugePages" > and "ShmemPmdMapped" entries really mean, and make it clear that there > are no other entries for other THP/folio sizes or mappings. > > Link: https://lore.kernel.org/all/20260225232708.87833-1-ak@linux.intel.com/ > Cc: Andrew Morton > Cc: Lorenzo Stoakes > Cc: Zi Yan > Cc: Baolin Wang > Cc: Liam R. Howlett > Cc: Nico Pache > Cc: Ryan Roberts Cc: Dev Jain > Cc: Barry Song > Cc: Lance Yang > Cc: Jonathan Corbet > Cc: Shuah Khan > Cc: Usama Arif > Cc: Andi Kleen > Signed-off-by: David Hildenbrand (Arm) > --- Makes sense to me. Feel free to add: Reviewed-by: Lance Yang