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V" , Nick Piggin , Peter Zijlstra , Russell King , Catalin Marinas , Brian Cain , WANG Xuerui , Geert Uytterhoeven , Jonas Bonn , Stefan Kristiansson , Stafford Horne , Michael Ellerman , Naveen N Rao , Paul Walmsley , Albert Ou , Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Andy Lutomirski , Bibo Mao , Baolin Wang , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Qi Zheng , Vishal Moola , "Aneesh Kumar K . V" , Kemeng Shi , Lance Yang , Peter Xu , Barry Song , linux-s390@vger.kernel.org, Guo Ren , Christophe Leroy , Palmer Dabbelt , Mike Rapoport , Oscar Salvador , Alexandre Ghiti , Jisheng Zhang , Samuel Holland , Anup Patel , Josh Poimboeuf , Breno Leitao , Alexander Gordeev , Gerald Schaefer , Hugh Dickins , David Hildenbrand , Ryan Roberts References: <20240730064712.3714387-1-alexs@kernel.org> Content-Language: en-US From: Alex Shi In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/15/24 1:13 AM, Matthew Wilcox wrote: > On Tue, Jul 30, 2024 at 02:46:54PM +0800, alexs@kernel.org wrote: >> We have struct ptdesc for page table descriptor a year ago, but it >> has no much usages in kernel, while pgtable_t is used widely. > > Hum, I thought I responded to this to point out the problem, but > I don't see the response anywhere, so I'll try again. > >> The pgtable_t is typedefed as 'pte_t *' in sparc, s390, powerpc and m68k >> except SUN3, others archs are all same as 'struct page *'. > > And there's a very good reason for that. On s390 and powerpc (I cannot > speak to the sparc/m68k), each page table is (potentially) smaller > than PAGE_SIZE. So we cannot do what your patch purports to do, as > we would not know whether we're referring to the first or subsequent > page tables contained within a page. >> Maybe at some point in the distant future we'll be able to allocate > a ptdesc per page table instead of per page allocated for use by page > tables. But we cannot do that yet. Got it. Thanks a lot for the info!