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b=XWzv7yYPoIuMX44YD8j0VCMsdDvMOX4ZVAIwX6BWM0BUqWc3RxIQZSbE4cGZBLrge gWLBh7F6BN09sSHOwzXLTPhMBdbgGZ6ISWHW4/1i53Zn5SSXa2PnleA4qBPK1HJpi/ etoE+9oM5tkUI97Gx9MHEzowWO3SL5laHbhNb2bs+YqJnehf7FqQ+20aklCnDvyxBU dQufrR0quNaM8Nwo+uAfom4D3GQWDgMFE29WL99bcadsidF86S38WdLPg0fZu1yARz kesEf0L+KRr0RP7uSr/Fj7nY9fKSeYTI9jz8Iy6In6IVSX3cWmDThsfmnJAvkoqJYQ 5vOTP2yUpOXvw== Date: Wed, 23 Sep 2026 09:15:57 +0100 From: "Lorenzo Stoakes (ARM)" To: Lance Yang Cc: akpm@linux-foundation.org, david@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, usama.arif@linux.dev, kas@kernel.org, guoren@kernel.org, bcain@kernel.org, geert@linux-m68k.org, dinguyen@kernel.org, schuster.simon@siemens-energy.com, jonas@southpole.se, stefan.kristiansson@saunalahti.fi, shorne@gmail.com, dalias@libc.org, glaubitz@physik.fu-berlin.de, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, linux@armlinux.org.uk, vgupta@kernel.org, monstr@monstr.eu, chris@zankel.net, jcmvbkbc@gmail.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, davem@davemloft.net, andreas@gaisler.com, richard.henderson@linaro.org, mattst88@gmail.com, linmag7@gmail.com, catalin.marinas@arm.com, mark.rutland@arm.com, chenhuacai@kernel.org, kernel@xen0n.name, tsbogend@alpha.franken.de, James.Bottomley@hansenpartnership.com, deller@gmx.de, maddy@linux.ibm.com, mpe@ellerman.id.au, chleroy@kernel.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, richard@nod.at, anton.ivanov@cambridgegreys.com, johannes@sipsolutions.net, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, ysato@users.sourceforge.jp, shakeel.butt@linux.dev, corbet@lwn.net, rdunlap@infradead.org, 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, hughd@google.com, qi.zheng@linux.dev, linux-doc@vger.kernel.org Subject: Re: [PATCH v4 04/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU arm Message-ID: References: <20260922-rcu-pagetable-freeing-v4-4-fe1ad1f1e303@kernel.org> <20260923080523.9480-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923080523.9480-1-lance.yang@linux.dev> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: EA51E40005 X-Stat-Signature: bmepnsx984g3p1a6t7g7hbqiy3zt7jfb X-Rspam-User: X-HE-Tag: 1790151381-609346 X-HE-Meta: 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 cdvEI5oj LpyRwETMrmg4XtXDYypfsdlWKJ8MxWqMWJlvq0uRAVY7aLDEdX5/44tXS47sOIUnEsUyE7D7bKke6h6KpqMbwOWVSiJSZ5k1pGlqabcfXCA1E+r6jGRA93lNb8ObGTdh1XPw4q1lFsAyXCYgzDQQ9UvFCJ1mlEGf+B3WJrD5ebj/q1BRLJ2BZX7+EsTH725QxAelf8/iL6Qr/oPpsFD3bnTFd0avrASYHaV14Ys3EJjW9W/nWauyBhNnnH7GPo+R1x4Fk6DitDaZn6N048XUmEzO3UT1rjzaLyqjVtNmM8hp8oqry3DEA+8d/OTXZ3Tb2n6518SIuoYJ/AFbr0ir7hI2kezEY6JAkx1x9j+0rknBddhMRK6HKhYY1kfOvQ0cSGFI5aN8FnAVrmTbw3jWZtFky5oc5av8MtB5KBPEczH9lYws286Qv+AdUJQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 23, 2026 at 04:05:23PM +0800, Lance Yang wrote: > > On Tue, Sep 22, 2026 at 04:35:35PM +0100, Lorenzo Stoakes (ARM) wrote: > >Commit a0ad5496b2b3 ("arm: mm: enable HAVE_RCU_TABLE_FREE logic") enabled > >CONFIG_MMU_GATHER_RCU_TABLE_FREE (then named HAVE_RCU_TABLE_FREE) for SMP > >arm architectures with LPAE enabled. > > > >Regardless of whether CONFIG_ARM_LPAE is enabled or not, the same page > >table freeing functions __pte_free_tlb() and __pmd_free_tlb() are used. > > > >Non-LPAE PMD page tables are folded into the PGD and freed by > >pgd_free() (PGD freeing is not part of mmu_gather page table freeing in any > >case), so this is a noop in this case. > > > >Since commit 358d1c39c82a ("arm: convert various functions to use ptdescs") > >both LPAE and non-LPAE PTE page table freeing uses tlb_remove_ptdesc(). > > > >Thus all page table freeing is performed under RCU with > >CONFIG_MMU_GATHER_RCU_TABLE_FREE enabled for LPAE and non-LPAE and thus it > >need not be gated on LPAE. > > > >A UP arm system can set CONFIG_PREEMPT_RCU, so a future pure RCU page > >table walker requires MMU_GATHER_RCU_TABLE_FREE to be enabled on UP as > >well, even if concurrent GUP fast is not possible there. > > > >Therefore, it is both safe and desirable to set > >CONFIG_MMU_GATHER_RCU_TABLE_FREE for all MMU arm architectures (nommu does > >not perform mmu_gather operations). > > > >This forms part of an overall effort to switch every architecture to this > >mode. > > > >Acked-by: Kiryl Shutsemau (Meta) > >Signed-off-by: Lorenzo Stoakes (ARM) > >--- > > Tested under heavy page-table teardown load on qemu-system-arm, > with and without ARM_LPAE. No issues seen :D > > Tested-by: Lance Yang > > Also, feel free to add: > > Acked-by: Lance Yang Thanks, much appreciated! :) > > > > arch/arm/Kconfig | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > >diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > >index 408aa58a2a5b..72b9afc6ae10 100644 > >--- a/arch/arm/Kconfig > >+++ b/arch/arm/Kconfig > >@@ -134,7 +134,7 @@ config ARM > > select HAVE_PERF_REGS > > select HAVE_PERF_USER_STACK_DUMP > > select HAVE_POSIX_CPU_TIMERS_TASK_WORK > >- select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE > >+ select MMU_GATHER_RCU_TABLE_FREE if MMU > > select HAVE_REGS_AND_STACK_ACCESS_API > > select HAVE_RSEQ > > select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7 && !KASAN > > > >-- > >2.55.0 > > > > -- Cheers, Lorenzo