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Wed, 23 Sep 2026 13:16:40 +0000 X-Mizu-Trace-ID: acd8da373ac6bf50 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 09/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-motorola Date: Wed, 23 Sep 2026 21:16:34 +0800 Message-ID: <20260923131634.47896-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20260922-rcu-pagetable-freeing-v4-9-fe1ad1f1e303@kernel.org> References: <20260922-rcu-pagetable-freeing-v4-9-fe1ad1f1e303@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0703D1C0006 X-Stat-Signature: ekyjpbjo18ihtunh69dyuptgowe4zyyp X-HE-Tag: 1790169404-344200 X-HE-Meta: U2FsdGVkX18D4eiaa/qvMPd3lB23S19ps5edGqVBrhkcFX6DPfFpykJ4ZNaJgWIGQsAnwoDTr7Y96Ub+JIxXPN3LuSPeMbTc8WjB/an17caLV8PYQJeJjiGrOmxR1X3nHHw98LZWxKlcXoYdqHGyIIB47R+RGc0DPH1pb0KEZ+5YFyn1lvUthZ4OnspBl7+Jpwygy/z6TNPOG6qze/Z/kW0ZdgbC0G1kMWv2Wv3ansEz2AVyK/2q7tg+2iHFTOd8msLKGbT2t64YoZxaoAMyBWg204kbV+MGbISNODX85EtzsedZ0scoOV3E+WMlTUVydLVWrsEe51jm+R+L+z1HS5dokyjtHJH7JBW1VR6Ek00Yp8ht+iCR5oYLIedtSKPGkPqzmvsgQJmU8g7yl4D3pYUVVaJAShTmqtc4Bx4HNPn5vt+U4O7i220CLBiZ1xpqfHEJUmrQDRh3/qgRomVj1fnlZFTBGOAnOPBhvoW7vABzK5h/6w9NpBaJtxVzLQ+XXVTobL2+Ote5WoP5OJcpSW1RBVM3a0giJJJI+LQ22un5KvuHwYDvUlqJaqKN3N0T+/iz2vPosfeYnP5+rzwGmv1V1ZJN1AD/xA4Vlo1b0K0XOMnsVVlgk/i+/nvHwikzeAGZyAQLG56aXGkfSDItC3JE4GvQKtyQ3Z+DDkMsVucEdgOrcZtFNYKZwe+SRblry3ax9Q0Bd2ndBSfA6lLhnd472if/k88SAU26Ou34ZwRLNL4EsDCvxk853+oVnTZeYes7NFLBFDWMDWi02FrOWO/LMcHd3PZalD0PESbyLaPb/Zb92SlTs8Dv11KjnMRVAI+YRjCiMpysIQODCc1GvQ2JeS/lAETZJtgoxvj4BfvB7z9u2f/RMCsLmVXkzGUlxP+fn1w07Kq3j9ehXcbr5ajJ4qrlHgoiPcSSoD26+X+dBENLk6qbZk9DjCqcSeZhg6pLDPihP2TBdvMbmKQ GBxIiuAB 01LTBHIEvg1HO6yX8M9H+8fGiC2NBVGCxBu50ZvDwb2TyePVzlDry7WahOYINb9LWpbbQ/AFU73PLoWi80Z1pMHgADdWTE3nJ+VumnZEzn8kF5CyOssmbw33aIlwr8u4OVC+YFF41VhvIjcuhIHPc8p/qRV/UqT0PJecg9OreiDIMgexoSrekLjH9T/limFl+tJw4nKLGiDESVUMdpBwiaVRE1kfCk2kBzcqxHRhBKET/9kZ12mFmt1ckgRZEpkp8IwCxLdSKS7lA5qoHyfhYHHihk3H0vi1r19yYvlGjfhrP1AqIc3Gw37dN99gZLj3s+brP1yvx/vnxuG8xiy8UxhCVIPpxjoppSty6pSPWiZ5lmC3V2wd/VeV50BUTCFrpmQmxi0ivnS2DJj4etaMRbkKdxGAtGVf3gBTX 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 04:35:40PM +0100, Lorenzo Stoakes (ARM) wrote: >sun3 and coldfire are already supported, however motorola requires a little >more care. > >Here, custom table removal logic is required, so >CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE is enabled for m68k-motorola. > >Firstly as part of this change, the page table level must be communicated >to the underlying __tlb_remove_table() implementation. > >Take advantage of the fact that page tables are aligned by more than enough >to permit setting TABLE_PTE or TABLE_PMD in the low bits of the pointer, >and store this there. > >Then update __pte_free_tlb() and __pmd_free_tlb() to pass this through, >then have __tlb_remove_table() decode this and pass it to >free_pointer_table(). > >The page table freeing is performed via call_rcu(), so free_pointer_table() >now will be invoked from softirq context, and as such may be re-entrant. > >Introduce an irq save/restore spinlock to handle this, and hold it over the >time a given ptable entry is being referenced in both get_pointer_table() >and free_pointer_table(). > >In order to make things a little easier in this respect, separate out the >logic for adding a new ptable entry into add_pointer_table() and only hold >the lock during ptable entry insertion in this case. > >Note that original list_add_tail(new, dp) added new prior to dp, which is >ptable_list[type].next, i.e. after ptable_list[type]. > >The equivalent therefore is list_add(new, &ptable_list[type]), which adds >new after ptable_list[type], only without needing to make reference to dp. > >Note that, as m68k-motorola specifies CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE, it >does not enable CONFIG_PT_RECLAIM. This isn't meaningfully impactful. > >With this applied, all of m68k implements CONFIG_MMU_GATHER_RCU_TABLE_FREE. > >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) >--- I wondered about slot reuse during the RCU wait, but that can't happen :) The slot stays marked busy until free_pointer_table() runs after RCU, and the last free unlinks the page under ptable_lock. Also ran page-table teardown stress and fork/exec churn on qemu-system-m68k (virt, m68040, CONFIG_MMU_MOTOROLA=y). All 40 rounds ran cleanly :D Acked-by: Lance Yang Tested-by: Lance Yang