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Thu, 20 Aug 2026 06:52:55 -0400 (EDT) Date: Thu, 20 Aug 2026 11:52:54 +0100 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: akpm@linux-foundation.org, ljs@kernel.org, nico.pache@linux.dev, baolin.wang@linux.alibaba.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com, rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, ziy@nvidia.com, usama.anjum@arm.com, agordeev@linux.ibm.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, jannh@google.com, willy@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH 01/57] mm: add pte_folio() Message-ID: References: <20260816224609.308019-1-kirill@shutemov.name> <20260816224609.308019-2-kirill@shutemov.name> <7e40cdfe-67d2-4ddf-a048-f33b2d590371@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7e40cdfe-67d2-4ddf-a048-f33b2d590371@kernel.org> On Tue, Aug 18, 2026 at 07:09:48PM +0200, David Hildenbrand (Arm) wrote: > On 8/17/26 00:45, Kiryl Shutsemau wrote: > > From: "Kiryl Shutsemau (Meta)" > > > > Callers that want the folio behind a present PTE spell it out as > > page_folio(pte_page(pte)). > > > > Add pte_folio() as the folio companion to pte_page(), and convert the > > callers in fs/proc/task_mmu.c and mm/hugetlb.c. > > > > Preparation for the anonymous collapse engine, which reads the folio > > behind a PTE in several places. > > [...] > > > > > +/** > > + * pte_folio - Return the folio mapped by a present PTE. > > + * @pte: A present page table entry. > > + * > > + * The folio companion to pte_page(); only meaningful for a present PTE > > + * that maps a struct-page-backed folio. > > + * > > + * Return: The folio containing the page @pte maps. > > + */ > > +static inline struct folio *pte_folio(pte_t pte) > > +{ > > + return page_folio(pte_page(pte)); > > +} > > There is a reason why most code doesn't need that: because they should be using > vm_normal_page() / vm_normal_folio(), or need the exact page and handle special > ptes differently (see gup.c that uses pte_page()). > > And other code that uses pte_page() doesn't really operate on folios AFAIKs. Fair. pte_folio() does not fit the abstraction as it stands, so I will drop it. I thought that maybe we can rework vm_normal_*() to be a predicate on a page table entry, so if it returns true the caller can safely use pxx_folio(). It would be a cleaner interface in my opinion. vm_ops->find_normal_page() breaks the idea, though. Xen (being the single user of the vm_op) wants the special bit to indicate a custom translation to the page here. A bool cannot describe this. Ugh.. -- Kiryl Shutsemau / Kirill A. Shutemov