From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E92E837A843 for ; Thu, 17 Sep 2026 01:36:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789609003; cv=none; b=gLq3JtB8r/qucHqKeT3i/+T6MjlMiCgWFW72zEY9IoiioZ6Dv6UFR1epHVOCbYHoBzkAdnpYry4RTDiN7L0W1gXzyiFRelNKBXavOqrvzzLfJg+t/JG80RJF/2kh9oXANC5haeqKwJ7JUrlcj4wMobVL3ik+MpG6YACY/f/LQlI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789609003; c=relaxed/simple; bh=VtQxH7RzBoNQHrc3smFanDfHoWWi5cssxMsFL5rb9Tw=; h=Date:To:From:Subject:Message-Id; b=ZtB8E/oViHOaAjUHDZmtG0oQ7hvFqe44hUvqJx4DsJAmbq6yp46Ihx/2OKoNUtcw2/JEckd2Zf5pBh27TrrCOkfm6IUJarO6+AzoROF1EatxM/UfGt1dASXgTPTQ/YpzagHTcFSIGOceHg6+FhtcVjBpozgwHwh08B9Ts0PqYUU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=SigJlZuo; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="SigJlZuo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B34EF1F00893; Thu, 17 Sep 2026 01:36:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789609001; bh=7TJ94Wy2U7efkIcQYl9Z9NXYCBAm42MISD7NdDnQHmk=; h=Date:To:From:Subject; b=SigJlZuotCpNnUGD+rlN7ALb3LW9U9b8NuucaQeauetckBvKNUHy8DaLvBEc7vYpD WAjWCYEqHivvwWeN8Tmp4MK80z85VPHU/rX/+XngRkxcXahwVQzBMfny0kL18/tBSE BbAF5st2AFXPDh2tTgM/+KYu2Foh/scYGPrK6hgs= Date: Wed, 16 Sep 2026 18:36:41 -0700 To: mm-commits@vger.kernel.org,songmuchun@bytedance.com,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch added to mm-unstable branch Message-Id: <20260917013641.B34EF1F00893@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/sparse-vmemmap: drop the extra tail page from device DAX reservation has been added to the -mm mm-unstable branch. Its filename is mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Muchun Song Subject: mm/sparse-vmemmap: drop the extra tail page from device DAX reservation Date: Wed, 16 Sep 2026 14:43:39 +0800 The device DAX vmemmap population still reserves one extra tail vmemmap page after the head page. Drop that extra reservation and let the shared tail page cover all tail vmemmap pages after the head page, so DAX follows the same reservation model as HugeTLB. This reduces the reserved vmemmap pages for optimized DAX mappings to one and removes the now-unneeded first-tail population from the generic and powerpc paths to simplify the code as well. Link: https://lore.kernel.org/20260916064341.1825793-10-songmuchun@bytedance.com Signed-off-by: Muchun Song Signed-off-by: Andrew Morton Acked-by: Qi Zheng Cc: David Hildenbrand (Arm) Cc: Jonathan Corbet Cc: Lorenzo Stoakes Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Mike Rapoport (Microsoft) Cc: Nicholas Piggin Cc: Oscar Salvador Cc: Randy Dunlap --- arch/powerpc/mm/book3s64/radix_pgtable.c | 46 --------------------- include/linux/mm.h | 3 - mm/mm_init.c | 2 mm/sparse-vmemmap.c | 13 +---- 4 files changed, 7 insertions(+), 57 deletions(-) --- a/arch/powerpc/mm/book3s64/radix_pgtable.c~mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation +++ a/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -1218,39 +1218,6 @@ base_mapping: return 0; } -static pte_t * __meminit radix__vmemmap_populate_address(unsigned long addr, int node, - struct vmem_altmap *altmap, - struct page *reuse) -{ - pgd_t *pgd; - p4d_t *p4d; - pud_t *pud; - pmd_t *pmd; - pte_t *pte; - - pgd = pgd_offset_k(addr); - p4d = p4d_offset(pgd, addr); - pud = vmemmap_pud_alloc(p4d, node, addr); - if (!pud) - return NULL; - pmd = vmemmap_pmd_alloc(pud, node, 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, addr); - if (!pte) - return NULL; - radix__vmemmap_pte_populate(pmd, addr, node, NULL, NULL); - vmemmap_verify(pte, node, addr, addr + PAGE_SIZE); - - return pte; -} - int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn, unsigned long start, unsigned long end, int node, @@ -1297,7 +1264,7 @@ int __meminit vmemmap_populate_compound_ if (!pte_none(*pte)) { /* * This could be because we already have a compound - * page whose VMEMMAP_RESERVE_NR pages were mapped and + * page whose retained vmemmap page was mapped and * this request fall in those pages. */ next = addr + PAGE_SIZE; @@ -1318,16 +1285,7 @@ int __meminit vmemmap_populate_compound_ return -ENOMEM; vmemmap_verify(pte, node, addr, addr + PAGE_SIZE); - /* - * Populate the tail pages vmemmap page - * It can fall in different pmd, hence - * vmemmap_populate_address() - */ - pte = radix__vmemmap_populate_address(addr + PAGE_SIZE, node, NULL, NULL); - if (!pte) - return -ENOMEM; - - next = addr + 2 * PAGE_SIZE; + next = addr + PAGE_SIZE; continue; } --- a/include/linux/mm.h~mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation +++ a/include/linux/mm.h @@ -5167,7 +5167,6 @@ static inline void vmem_altmap_free(stru } #endif -#define VMEMMAP_RESERVE_NR 2 #ifdef CONFIG_ARCH_WANT_OPTIMIZE_DAX_VMEMMAP static inline bool __vmemmap_can_optimize(struct vmem_altmap *altmap, struct dev_pagemap *pgmap) @@ -5187,7 +5186,7 @@ static inline bool __vmemmap_can_optimiz * For vmemmap optimization with DAX we need minimum 2 vmemmap * pages. See layout diagram in Documentation/mm/vmemmap_dedup.rst */ - return !altmap && (nr_vmemmap_pages > VMEMMAP_RESERVE_NR); + return !altmap && (nr_vmemmap_pages > VMEMMAP_OPTIMIZATION_PAGES); } /* * If we don't have an architecture override, use the generic rule --- a/mm/mm_init.c~mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation +++ a/mm/mm_init.c @@ -1056,7 +1056,7 @@ static inline unsigned long compound_nr_ if (!section_vmemmap_optimizable(ms)) return pgmap_vmemmap_nr(pgmap); - return VMEMMAP_RESERVE_NR * (PAGE_SIZE / sizeof(struct page)); + return VMEMMAP_OPTIMIZATION_PAGES * (PAGE_SIZE / sizeof(struct page)); } static void __ref memmap_init_compound(struct page *head, --- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation +++ a/mm/sparse-vmemmap.c @@ -136,7 +136,6 @@ int __meminit section_nr_vmemmap_pages(u { const struct mem_section *ms = __pfn_to_section(pfn); const int order = section_compound_order(ms); - const int vmemmap_pages = pgmap ? VMEMMAP_RESERVE_NR : VMEMMAP_OPTIMIZATION_PAGES; const unsigned long pages_per_compound = 1UL << order; VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SUBSECTION)); @@ -147,13 +146,13 @@ int __meminit section_nr_vmemmap_pages(u if (order < PFN_SECTION_SHIFT) { VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, pages_per_compound)); - return vmemmap_pages * nr_pages / pages_per_compound; + return VMEMMAP_OPTIMIZATION_PAGES * nr_pages / pages_per_compound; } VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION)); if (IS_ALIGNED(pfn, pages_per_compound)) - return vmemmap_pages; + return VMEMMAP_OPTIMIZATION_PAGES; return 0; } @@ -521,17 +520,11 @@ static int __meminit vmemmap_populate_co if (!pte) return -ENOMEM; - /* Populate the tail pages vmemmap page */ - next = addr + PAGE_SIZE; - pte = vmemmap_populate_address(next, node, NULL, -1, flags); - if (!pte) - return -ENOMEM; - /* * Reuse the shared page for the rest of tail pages * See layout diagram in Documentation/mm/vmemmap_dedup.rst */ - next += PAGE_SIZE; + next = addr + PAGE_SIZE; rc = vmemmap_populate_range(next, last, node, NULL, page_to_pfn(page), flags); if (rc) _ Patches currently in -mm which might be from songmuchun@bytedance.com are mm-sparse-relax-struct-mem_section-size-constraints.patch mm-sparse-vmemmap-rename-hvo-order-macros.patch mm-mm_init-skip-initializing-shared-vmemmap-tail-pages.patch mm-sparse-vmemmap-initialize-shared-tail-vmemmap-pages-on-allocation.patch mm-sparse-vmemmap-support-section-based-vmemmap-accounting.patch mm-mm_init-factor-out-pfn_to_zone.patch mm-sparse-vmemmap-move-helpers-ahead-of-future-callers.patch mm-sparse-vmemmap-support-section-based-vmemmap-optimization.patch mm-sparse-initialize-memory-sections-earlier.patch mm-hugetlb-switch-hugetlb-to-section-based-vmemmap-optimization.patch mm-sparse-vmemmap-remove-sparsemem_vmemmap_preinit-support.patch mm-sparse-inline-usemap-allocation-into-sparse_init_nid.patch mm-sparse-remove-section_map_size.patch mm-hugetlb-remove-huge_bootmem_hvo.patch mm-hugetlb-remove-huge_bootmem_cma.patch mm-hugetlb-localize-struct-huge_bootmem_page.patch mm-hugetlb-localize-huge_bootmem_zones_valid.patch mm-sparse-vmemmap-introduce-config_vmemmap_optimization.patch mm-sparse-vmemmap-introduce-config_vmemmap_optimization-fix.patch mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch mm-sparse-vmemmap-open-code-init_compound_tail.patch mm-sparse-vmemmap-prepare-dax-vmemmap-population-for-compound-page-orders.patch mm-sparse-vmemmap-set-compound-page-order-for-device-dax.patch mm-sparse-vmemmap-switch-device-dax-to-shared-tail-vmemmap-pages.patch mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch mm-sparse-vmemmap-drop-the-extra-tail-page-from-device-dax-reservation.patch mm-sparse-vmemmap-drop-unused-section_nr_vmemmap_pages-arguments.patch documentation-mm-update-dax-vmemmap-deduplication-docs.patch