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b=oQwWOQkywYDf1JkmRsDbC/o6DR3oPInrHh+/leVHpzXY/fgKnBPlAbat4yOirXksi EWALa8XUeMd2tsIqTrSCJ0hISS3LcHe3D0i0Tgz4u8GN0a6ybM3BZinVZZLhG3Kwem I7b4mFWjjtLPtBFFyxKMPPiC1fv/6tqbKR6ms7bWmlQ8jqkRp5houN8+Tl0nlHq8Ok pNWxEWvRV+ENJCiZHISEOFERm2DQsybnZiI9c7WeH02xnMWwF75/9ODvNlEXLXkUxS 1sCqPrGh63gyzzgORCeokaPT4Set6v00jX6f1b6hgWldcMbm+rJMuLtgU0iQ1Yzy3g sAGIwJhyz9HZg== Date: Wed, 23 Sep 2026 14:21:56 +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 09/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-motorola Message-ID: References: <20260922-rcu-pagetable-freeing-v4-9-fe1ad1f1e303@kernel.org> <20260923131634.47896-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260923131634.47896-1-lance.yang@linux.dev> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: E04C3A0002 X-Stat-Signature: mhp7b4u17xwbex6o4186nr9eaaoi34sm X-Rspam-User: X-HE-Tag: 1790169742-73535 X-HE-Meta: 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 /ix8eWto /fa/JSS1OGmbPFXx49TkQIIwK65iSeDP1T/0E197x0AHC5NWhbASZJEPs/DYDJcksef04CJf5OrC4+RR4FjnUvBy3axOhXw/AUfYdyVjVZPsg99qHEe87iYkuWyQh10GfmFnLSpyGUPVI0xXMNiA6Z4FkWyueMwey58t2vnuqumV0VQWMjgfEjDWwnQifxDxUOA9UXsj+OpW6zDIN+RnViibHe7bzyswIeLj/3Lrdix5P6//t8jfJNspmuj1bG/A8139MMcE/c/C1ar0K0DFbmnazjzr88EkkuXOlZjGAtl34lLdQBIsELjeLCUzrqZsqj6fpETSkP0gwmB62c8IMloQoCrjib0QfBQXifJU1N/mV3pEiniTUTeNFDEOs5eOS/3hzYwRgSG6O8nG1XMp/EWKLb6E7dbxgS+Tfig1IFSEPtnLTKvvRwjbQVw== 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 09:16:34PM +0800, Lance Yang wrote: > > 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 Great, thanks! Really appreciate the testing :) -- Cheers, Lorenzo