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Howlett" , Nico Pache , Dev Jain , Barry Song , Shuah Khan , Usama Arif , Andi Kleen Subject: Re: [PATCH v2] docs: filesystems: clarify KernelPageSize vs. MMUPageSize in smaps In-Reply-To: <20260306081916.38872-1-david@kernel.org> References: <20260306081916.38872-1-david@kernel.org> Date: Mon, 09 Mar 2026 10:14:30 -0600 Message-ID: <87ms0hvv2x.fsf@trenco.lwn.net> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 34305120003 X-Stat-Signature: magayux1zrf37rqcuhdiaye3ji934ysj X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1773072873-301971 X-HE-Meta: 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 bLoYLCvO n3hLItLtqyq5EnsK8urDQi6EGO+yeLDqdCiugUTmWfzPULLTgkGfqWE3X6ueo8EIMpIKaZ9bJ5nDFCMjX3srAPNa9COuakteBtJ7M+E0yYgnU4Jhylsuu0MrIUgImM3fyIQEdlysbs9zLI5EP4Nu2m4z5zs3XrwWSaH1ISyajBb4sXZWlJ2DQGKYkCfkEL+HQxGetPkfRi/lB8+4wSwAegYHJ1XpXFLEEH7xqVuemtmMJSUkXVEqlQ42f9knatwT48Gzr8FA9W6QjBLSm7w4feROzKg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: "David Hildenbrand (Arm)" writes: > 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. > > Also drop the duplicate "KernelPageSize" and "MMUPageSize" entries in > the example. Applied, thanks. jon