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Wed, 23 Sep 2026 08:05:34 +0000 X-Mizu-Trace-ID: 0dc515f7c86dd02d X-Migadu-Flow: FLOW_OUT From: Lance Yang To: ljs@kernel.org 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, lance.yang@linux.dev, 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 Date: Wed, 23 Sep 2026 16:05:23 +0800 Message-ID: <20260923080523.9480-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20260922-rcu-pagetable-freeing-v4-4-fe1ad1f1e303@kernel.org> References: <20260922-rcu-pagetable-freeing-v4-4-fe1ad1f1e303@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 546BB180002 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: ftxf1w3991u33t6pjt3ym1fw7gbtfxbh X-HE-Tag: 1790150746-167542 X-HE-Meta: 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 VZAXwjTs XWSSmYMZnlG3pvGwRiTLNk6MIrbHTtYai4oY2tKz/pxsN6xLLQnw6oHZJjqBOW6fysuSOR5jkoltX+zzuBUDxbHcvdasQaGLVBpcNN9BPJcqYMsD8fdCyWh43ZRSvRGyCnGNg9QO8fnJ+94/scCcIAHDey+bP/Pm4VhyAEnBlMbGE2otgyIPnPC75D422VZfJDcXqoB2t+CExteyNE2D4xrI2SRvlNcpi9U2Fv1Gastv7G4xcz17KPqu+U9wrNoVu4/R4bmHywkPz5Q+jDzyGMY3TWyPojSQFVtfzGLeWQoWRwdrX7cXyEA7HzFm/IwdOhEvTPmQpalpD/ErNiz0wrjYPEx9CZUWF/r4ICerFfvkoVjBVo8k8BK5Nj3r0ODFz4k924+Dmdq0C8drh9s6zNnH6gfy4LG408UJ1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 > 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 > >