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Tue, 1 Sep 2026 13:11:59 -0400 (EDT) Date: Tue, 1 Sep 2026 18:11:57 +0100 From: Kiryl Shutsemau To: "Lorenzo Stoakes (ARM)" Cc: Jason Gunthorpe , Andrew Morton , David Hildenbrand , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Guo Ren , Brian Cain , Geert Uytterhoeven , Dinh Nguyen , Simon Schuster , Jonas Bonn , Stefan Kristiansson , Stafford Horne , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Russell King , Vineet Gupta , Michal Simek , Chris Zankel , Max Filippov , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , "David S. Miller" , Andreas Larsson , Richard Henderson , Matt Turner , Magnus Lindholm , Catalin Marinas , Mark Rutland , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , "James E.J. Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Richard Weinberger , Anton Ivanov , Johannes Berg , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnd Bergmann , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , John Hubbard , Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-snps-arc@lists.infradead.org, linux-arch@vger.kernel.org, sparclinux@vger.kernel.org, linux-alpha@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-um@lists.infradead.org, Hugh Dickins , Qi Zheng Subject: Re: [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period Message-ID: References: <20260901-rcu-pagetable-freeing-v1-0-5456a81c8212@kernel.org> <20260901-rcu-pagetable-freeing-v1-1-5456a81c8212@kernel.org> <20260901142408.GA56830@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: CB06FA0009 X-Stat-Signature: 3bwd5r83x6gmic68f3gnydbzwppwq3ih X-Rspam-User: X-HE-Tag: 1788282744-855927 X-HE-Meta: U2FsdGVkX1/Z187kBv+ux6DwANalu5wXkQ91Yu5AE0as4rDvzxcm8JuOE/GyllcDZ/68KCT56Z9sfEfZYYG9DoGtGRQFSutJqWnMQeqrhS86OKpVJ7+N1l7CsP1SKwmPjpVBldBi/P7os6BnO/fhU6rQtsaQdFFPeSL/hMTzTEEESbxMdC16N9Z5um9VF1xZW5L67oKC+qeKNIb4gB1AMW2nrU7Dt2hRmbV2OLu3JxupWlH1VDlnkV8vcWzkcwjRY013Ld7u68tSoam4rXbRJnZWWZzEzE5PhqkT2oMyzTiIe9MwHvpSNQCmkY3IvYZ+MMiATlFzUlq6rsgGgpK7fE089DenyLj0u7LkpX7P4jH90PWsXR+7skCMULLE5gO13p9njCktrPS35l6lN8g8tSSmbi55rh4T9gmZnRsj+DkLhRbzFXYqkfvP4gcqXO0gAclu37l+ek7J+ASzy8Vg62ztVDtgP7JDXfvshf3F729UK6H5DZJXWxIS8UNXUMyW5mDxNCBq0R4fL4NEnlE4RCT+UadtBgRfsKgzqXLVnw+yTgvPWC6Vb7Z8xfIS5fAiqJgDEN6udplvYn12y+AhqKYlIB/ppqhcRGTq1SmMD1QNrXDuUeNhx6dc0ulpRz5GyYh8D9N9msSuIWve5/ErUpvRm3fh27taTJJuTtUrqABo6gSzRXYbICAta//lSO0B/fHOIs/l1HPhUPbG1LDqc0K5/9j2KKSzXryVA94LJ6Du7dLbwJ3RNnJ4RupL6zLzHi3R2es1+OV9RiZQzg1LVVGQmfCAeECS5sIlvUa/0m4VPGceLdAtPZS2js+ap8BdKYjsIxJOShGidH5f0LIQt8ugpnK7y+E84BepzdwITGSV5xP7tUVD94EnWtYucr43I175SLnjRAtURNRSiQzZVLe4rrT6/dK+zNFXThf4+aR3PiYPnf+4lCwAZQm15dJy4YIBAuXCVV3Q0O0kZYb dyPOecRJ Ok6MCyOO2LiVqBS1amBjMenKVGCTqyH2U4SUo3hjxF8THYSzv3cSjLFKohtfPwaRG7HiVwjmKjCj9jSnQSo0kk61ijYl/cviBUr9cEpVMFgzWhbRuSbu8/0u0uQCLRgdv/cR8KZ8zRngEK6T/QSRau3h7HtQ9v+YpamrZxakNEfcki6F15q6gdjWHfq6QkliVRPrlxwirtN5MADz++SBENBbEeMjrGwwKxY3wPJsUGnfJbGXt7N6U3YFf+Tl+QIB0nyC7CsTh733QZliCc4pjD61fvI6j65f4nVt16n5MFXeTBx+Mqiz7Ya0Uz1vFq1X1eUR9KvQvsxNoMN2aT23lYHWwcqQgaIn/ZAzwJBsisiY4i9oaWxynC+DMGNYEAmte0QRe4bectaOHbhK0ChgHa3K2Vw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 01, 2026 at 04:45:14PM +0100, Lorenzo Stoakes (ARM) wrote: > > munmap() of 64G worth of THP should be enough to demonstrate the > > problem. > > I mean you're going to hit that from RCU freeing page tables already, which > most architectures already do right? Not at the same rate -- tlb_remove_table() batches into struct mmu_table_batch. One call_rcu() per MAX_TABLE_BATCH. > So if RCU saturation is a problem, that problem already exists, but I've > not heard of that being a problem at all? I did quick test and I don't see a measurable difference in munmap() wall time of 40G of THPs. I see ~17x more softirqs, but this is expected. The objection is retracted. We can return to this later if it is going to be visible anywhere. -- Kiryl Shutsemau / Kirill A. Shutemov