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Wed, 23 Sep 2026 11:54:26 +0000 X-Mizu-Trace-ID: b457f4ea14dabe32 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 08/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sh-X2 Date: Wed, 23 Sep 2026 19:54:17 +0800 Message-ID: <20260923115417.34112-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20260922-rcu-pagetable-freeing-v4-8-fe1ad1f1e303@kernel.org> References: <20260922-rcu-pagetable-freeing-v4-8-fe1ad1f1e303@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: tyr1csx6u9rnkdfwkmfhxcgi9cbxykzf X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 8BBDE40009 X-HE-Tag: 1790164471-34056 X-HE-Meta: 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 LDPYefXA +QxT9rO3edW5QyVSM8YcV/5sqTCR7RC8nf2nMd1Em0jxFWE4a3CXVyzFQOkC+SVcyQVgz84fkoz4HsTs+2tR6Acj1vkHBTtIFs9ag/KX6lj09nsSDndgdUH6cKpT+ZR2GuYysyKgVMDYAxRytR299L46voxxatH7hy1sxgr2GCLNGWxu4Pz6C+t8ApRZs9RJDNIXvorozYxaQZ/ACvxekcEWzfPFSb9Uj+ojtcA8Xrzkj8DzPBzQGhicjgHOivJ3KRaAr2cjvCd6kA+Mguo0Xq9m0JgzXoBWHuecuy4dwGFtooioDkJsTlmABPBS6rYU0cR4oszs3c1K3uZXVG6PrrEh1rf2zlNJqk5lS90reyPtlqEXOAEegCzwp7nAbFBa2EYfC 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 04:35:39PM +0100, Lorenzo Stoakes (ARM) wrote: >Currently, non-x2 sh specifies CONFIG_MMU_GATHER_RCU_TABLE_FREE allowing >RCU page table freeing. > >sh-X2 is problematic because it utilises slab-allocated PMD page tables, >and thus tlb_remove_ptdesc() cannot be used in these cases. > >All other sh variants are fine as commit e3ecf7c7d082 ("mm: pgtable: >convert some architectures to use tlb_remove_ptdesc()") already converted >page table freeing to use tlb_remove_ptdesc(), which does so after an RCU >grace period when CONFIG_MMU_GATHER_RCU_TABLE_FREE is specified. > >Resolve this issue by firstly specifying CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE >for sh-X2, so the arch can provide its own __tlb_remove_table() >implementation (called after the RCU grace period). > >Then, convert __pmd_free_tlb() to tag the pointer to the PMD, and have >__tlb_remove_table() check this tag to determine whether to free via the >slab or to use pagetable_dtor_free(). Makes sense to me, so RCU callback won't mistake a slab PMD for a PTE page :) >This follows the pattern used by sparc64 as implemented in commit >4a0100f7546f ("sparc64: use RCU page table freeing"). > >Previously __pmd_free_tlb() freed PMD page tables immediately, before any >TLB flush IPI. This seems to be a pre-existing bug, which this change also >resolves. > >CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE is only specified for sh-X2, as setting >it disables CONFIG_PT_RECLAIM and causes __tlb_remove_table_one() to call >tlb_remove_table_sync_rcu() and synchronize_rcu() in turn, and this is not >necessary for other sh variants. > >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) >--- LGTM, feel free to add: Acked-by: Lance Yang