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([2001:1a48:8:903:1ed6:4f73:ce38:f9d4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4851fae4a68sm24849435e9.9.2026.03.05.01.03.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2026 01:03:13 -0800 (PST) Message-ID: <8011ab29-de9b-4a9e-b437-a514f6e462a0@suse.com> Date: Thu, 5 Mar 2026 10:03:11 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] docs: filesystems: clarify KernelPageSize vs. MMUPageSize in smaps Content-Language: en-US To: "David Hildenbrand (Arm)" , linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , Zi Yan , Baolin Wang , "Liam R . Howlett" , Nico Pache , Dev Jain , Barry Song , Lance Yang , Jonathan Corbet , Shuah Khan , Usama Arif , Andi Kleen References: <20260304155636.77433-1-david@kernel.org> From: Vlastimil Babka In-Reply-To: <20260304155636.77433-1-david@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/4/26 16:56, 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) Acked-by: Vlastimil Babka (SUSE) Thanks.