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Wed, 30 Sep 2026 07:08:31 -0700 (PDT) From: Muchun Song To: Andrew Morton , David Hildenbrand , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Muchun Song , Lorenzo Stoakes , Mike Rapoport , Qi Zheng , Nicholas Piggin , Christophe Leroy , Ritesh Harjani , Shrikanth Hegde , Randy Dunlap , Muchun Song , Lance Yang Subject: [PATCH v6 09/12] powerpc/mm: switch device DAX to shared tail vmemmap pages Date: Wed, 30 Sep 2026 22:06:24 +0800 Message-ID: <20260930140627.57431-10-songmuchun@bytedance.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260930140627.57431-1-songmuchun@bytedance.com> References: <20260930140627.57431-1-songmuchun@bytedance.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The powerpc radix compound vmemmap population path still finds a reusable tail page by walking the vmemmap page tables. Switch it to the common vmemmap_shared_tail_page() helper instead, so it can use the shared vmemmap page directly to simplify the code. This removes the powerpc-specific tail-page lookup and its fallback path and aligns the device DAX vmemmap optimization path with HugeTLB. Signed-off-by: Muchun Song Acked-by: David Hildenbrand (Arm) --- v6: - Collect Acked-by from David Hildenbrand --- arch/powerpc/mm/book3s64/radix_pgtable.c | 80 +++--------------------- include/linux/vmemmap-optimization.h | 6 ++ mm/sparse-vmemmap.c | 6 -- 3 files changed, 15 insertions(+), 77 deletions(-) diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c index cf692b2b5f7b..ee068f24a79f 100644 --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include @@ -1250,59 +1251,6 @@ static pte_t * __meminit radix__vmemmap_populate_address(unsigned long addr, int return pte; } -static pte_t * __meminit vmemmap_compound_tail_page(unsigned long addr, - unsigned long pfn_offset, int node) -{ - pgd_t *pgd; - p4d_t *p4d; - pud_t *pud; - pmd_t *pmd; - pte_t *pte; - unsigned long map_addr; - - /* the second vmemmap page which we use for duplication */ - map_addr = addr - pfn_offset * sizeof(struct page) + PAGE_SIZE; - pgd = pgd_offset_k(map_addr); - p4d = p4d_offset(pgd, map_addr); - pud = vmemmap_pud_alloc(p4d, node, map_addr); - if (!pud) - return NULL; - pmd = vmemmap_pmd_alloc(pud, node, map_addr); - if (!pmd) - return NULL; - if (pmd_leaf(*pmd)) - /* - * The second page is mapped as a hugepage due to a nearby request. - * Force our mapping to page size without deduplication - */ - return NULL; - pte = vmemmap_pte_alloc(pmd, node, map_addr); - if (!pte) - return NULL; - /* - * Check if there exist a mapping to the left - */ - if (pte_none(*pte)) { - /* - * Populate the head page vmemmap page. - * It can fall in different pmd, hence - * vmemmap_populate_address() - */ - pte = radix__vmemmap_populate_address(map_addr - PAGE_SIZE, node, NULL, NULL); - if (!pte) - return NULL; - /* - * Populate the tail pages vmemmap page - */ - pte = radix__vmemmap_pte_populate(pmd, map_addr, node, NULL, NULL); - if (!pte) - return NULL; - vmemmap_verify(pte, node, map_addr, map_addr + PAGE_SIZE); - return pte; - } - return pte; -} - int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, unsigned long start, unsigned long end, int node, @@ -1320,6 +1268,12 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, pud_t *pud; pmd_t *pmd; pte_t *pte; + struct page *tail_page; + unsigned int order = pfn_to_section_compound_order(start_pfn); + + tail_page = vmemmap_shared_tail_page(order, device_zone(node)); + if (!tail_page) + return -ENOMEM; for (addr = start; addr < end; addr = next) { @@ -1349,10 +1303,9 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, next = addr + PAGE_SIZE; continue; } else { - unsigned long nr_pages = pgmap_vmemmap_nr(pgmap); + unsigned long nr_pages = 1UL << order; unsigned long addr_pfn = page_to_pfn((struct page *)addr); unsigned long pfn_offset = addr_pfn - ALIGN_DOWN(addr_pfn, nr_pages); - pte_t *tail_page_pte; /* * if the address is aligned to huge page size it is the @@ -1377,23 +1330,8 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, next = addr + 2 * PAGE_SIZE; continue; } - /* - * get the 2nd mapping details - * Also create it if that doesn't exist - */ - tail_page_pte = vmemmap_compound_tail_page(addr, pfn_offset, node); - if (!tail_page_pte) { - - pte = radix__vmemmap_pte_populate(pmd, addr, node, NULL, NULL); - if (!pte) - return -ENOMEM; - vmemmap_verify(pte, node, addr, addr + PAGE_SIZE); - - next = addr + PAGE_SIZE; - continue; - } - pte = radix__vmemmap_pte_populate(pmd, addr, node, NULL, pte_page(*tail_page_pte)); + pte = radix__vmemmap_pte_populate(pmd, addr, node, NULL, tail_page); if (!pte) return -ENOMEM; vmemmap_verify(pte, node, addr, addr + PAGE_SIZE); diff --git a/include/linux/vmemmap-optimization.h b/include/linux/vmemmap-optimization.h index bd0974b262a4..fa9e9abd6656 100644 --- a/include/linux/vmemmap-optimization.h +++ b/include/linux/vmemmap-optimization.h @@ -83,6 +83,12 @@ static inline unsigned int pfn_to_section_compound_order(unsigned long pfn) { return 0; } + +static inline struct page *vmemmap_shared_tail_page(unsigned int order, + struct zone *zone) +{ + return NULL; +} #endif /* CONFIG_VMEMMAP_OPTIMIZATION */ static inline bool vmemmap_optimizable_pfn(unsigned long pfn) diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c index d40a2f5b5fca..e1f8a03e3d49 100644 --- a/mm/sparse-vmemmap.c +++ b/mm/sparse-vmemmap.c @@ -240,12 +240,6 @@ struct page __ref *vmemmap_shared_tail_page(unsigned int order, struct zone *zon return page; } -#else -static inline struct page *vmemmap_shared_tail_page(unsigned int order, - struct zone *zone) -{ - return NULL; -} #endif static __meminit void *vmemmap_alloc_pte(unsigned long pfn, int node, -- 2.54.0