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Mon, 09 Nov 2026 04:33:56 +0000 X-Mizu-Trace-ID: b7fb94620bed6bfe X-Migadu-Flow: FLOW_OUT From: Lance Yang To: songmuchun@bytedance.com Cc: david@kernel.org, maddy@linux.ibm.com, rppt@kernel.org, akpm@linux-foundation.org, lance.yang@linux.dev, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, ritesh.list@gmail.com, sshegde@linux.ibm.com, osalvador@suse.de, qi.zheng@linux.dev, muchun.song@linux.dev, chenhuacai@kernel.org, kernel@xen0n.name, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, x86@kernel.org, loongarch@lists.linux.dev, linux-s390@vger.kernel.org Subject: Re: [PATCH v3 3/5] loongarch/mm: disable device DAX vmemmap optimization Date: Mon, 9 Nov 2026 12:33:46 +0800 Message-ID: <20261109043346.38778-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261107043122.25650-4-songmuchun@bytedance.com> References: <20261107043122.25650-4-songmuchun@bytedance.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: 6i7zhayifj5rosqpomigx16endw6pn81 X-Rspamd-Queue-Id: 93B50100003 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794198837-608841 X-HE-Meta: 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 oYeHiKrw ZJqvEg2Z1klYSaX06rSKuvyGRqi+ppgaNNYmImR3mH+86zhL9nWXvwk5OIQK3gntIs1j68IrIqiq1Evh3OOuDPxlb4fbZOC2Cyy3/cZPjA1egcZrQkUQHm+LvkJjMZmiMHBaO81qZcDXDvIsA53xE4ugQ0kVx9oQqjGr3VNvijMxPFBZZyinXPpFEbKova+hMH3+M3K2rIdMYZJQb0411wLbyBgjvoLlcVl83N+PsznphaJDUQKG4xvcrV9oNl+FZd1LVo/IPbuvD9/snSNSvcLno17xGW1ubJEoN119vOBUbjNh4h3pF3/w1vj18ap5A3NJs10/SYV9RK1G2K9fTK4vjcAEFzMnRtQMk2VZoITKBV+X+lf2Y8ZRA4A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Sat, Nov 07, 2026 at 12:31:20PM +0800, Muchun Song wrote: >LoongArch selects ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP but not >ARCH_WANT_OPTIMIZE_DAX_VMEMMAP. Its vmemmap_free() implementation is also >empty, so it cannot tear down optimized Device DAX mappings. > >A later change removes the generic Device DAX architecture gate and lets >vmemmap_populate() decide whether a section can use optimization. Clear the >section compound order in the LoongArch path so Device DAX keeps using >unoptimized mappings. > >This does not affect HugeTLB HVO: LoongArch does not support gigantic >pages, so HugeTLB does not use section-based vmemmap optimization there. > >Signed-off-by: Muchun Song >--- >v2: >- New patch using section_vmemmap_optimization_disable() to keep Device > DAX vmemmap optimization disabled on LoongArch (reported by Sashiko) >--- > arch/loongarch/mm/init.c | 2 ++ > 1 file changed, 2 insertions(+) > >diff --git a/arch/loongarch/mm/init.c b/arch/loongarch/mm/init.c >index f801f7097f03..ea769e479241 100644 >--- a/arch/loongarch/mm/init.c >+++ b/arch/loongarch/mm/init.c >@@ -15,6 +15,7 @@ > #include > #include > #include >+#include > #include > #include > #include >@@ -143,6 +144,7 @@ void __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node, > int __meminit vmemmap_populate(unsigned long start, unsigned long end, > int node, struct vmem_altmap *altmap) > { >+ section_vmemmap_optimization_disable(start, end); Yeah, clearing the order here keeps Device DAX optimization disabled once the generic gate goes away ;) Nothing jumped out at me, feel free to add: Reviewed-by: Lance Yang