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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-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , Precedence: list X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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=unavailable autolearn_force=no version=4.0.1 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