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 75C583C81B2 for ; Wed, 30 Sep 2026 19:01:37 +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=1790794898; cv=none; b=mW9vw8UgNyyZWDoGyRiK+gtBNCgnrNCGvhTc1e135fAOStsW5/6ojzxOjL3gqkuYOX5GLgdsSv4rl8wrHDCW+V4HDkpy9R/7Cub4V0jIgobHwT8oaMd9vXjMxo9jMVUHpx8QLr2Z2Hi/9WVprV7v6iMx2PxW5fZxoztSxRb/49I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790794898; c=relaxed/simple; bh=+UhsRZU2Y/t6bzdv8x4wv4VSB5UHOb1cqr630+CmkXY=; h=Date:To:From:Subject:Message-Id; b=Uin0er6Ei5G5LVZwUz6Q/iL9qcPVpY1wI8bgPjL8kiecNyTRTM4T0tbpvCiLNJ6MuMk1fMi5RvLhh9wL2iSBRjA0xl4RQY0EBrFGV92XS2/3d895gYVhXnr3GUoVG9IH/k43KubnguK/o5HFuc9cWSN7sSYw0sX2Aih4icuaEDs= 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=qo3t4Kr0; 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="qo3t4Kr0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 33B831F000FF; Wed, 30 Sep 2026 19:01:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1790794897; bh=pXPqTvsm6laNUu7BLbFuVy6kG7T5Ptp/6UvQMnKYUKU=; h=Date:To:From:Subject; b=qo3t4Kr0DiUg4iYPN3vFY0BLCDtRjzozZb+4m/uvHyERvdCoO6/yHj/WI0bWDb9jX 7fs6h4toyUo0MN2HM3ytTHDSHpUqMkY6Vd966AWImBAK0bO6/GS8k/AAxg8RrIEQ/d 1jbyZ/UfGAWtWtx66XvT8hNKquHDgybO87EpbrAo= Date: Wed, 30 Sep 2026 12:01:36 -0700 To: mm-commits@vger.kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch added to mm-unstable branch Message-Id: <20260930190137.33B831F000FF@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: allocate shared tail page array dynamically has been added to the -mm mm-unstable branch. Its filename is mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.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-allocate-shared-tail-page-array-dynamically.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: allocate shared tail page array dynamically Date: Wed, 30 Sep 2026 22:06:17 +0800 Commit 622026e87c40 ("mm/hugetlb: remove fake head pages") added the per-zone vmemmap_tails array. Its size depends on MAX_FOLIO_ORDER, which had been moved to mmzone.h in preparation for the array. PUD_ORDER is defined by linux/pgtable.h, which cannot be included from mmzone.h without creating an include cycle. It was therefore open-coded as PUD_SHIFT - PAGE_SHIFT. This removed the dependency on PUD_ORDER, but not the underlying dependency on architecture page-table definitions. PUD_SHIFT is generally provided by architecture page-table headers, which are not guaranteed to have been included when mmzone.h is parsed. The dependency remained hidden because vmemmap_tails was originally guarded by CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP. Under that condition, MAX_FOLIO_ORDER resolves to either MAX_PAGE_ORDER or the fixed HugeTLB limit, rather than the PUD_SHIFT-based definition. Device DAX, however, does not require CONFIG_HUGETLB_PAGE. When it is converted to use section-based vmemmap optimization, MAX_FOLIO_ORDER can resolve to PUD_SHIFT - PAGE_SHIFT while it is being used to size vmemmap_tails. This would make struct zone depend on architecture page-table definitions being available when mmzone.h is parsed. Replace the embedded array with a pointer and allocate it on first use. This moves the order-count evaluation into sparse-vmemmap.c, after the architecture page-table definitions are available, and removes the dependency from mmzone.h. Removing the compile-time array also removes the original reason for keeping MAX_FOLIO_ORDER and the vmemmap optimization sizing definitions in mmzone.h. Follow-up cleanups can place each definition in the header owned by its respective subsystem. Link: https://lore.kernel.org/20260930140627.57431-3-songmuchun@bytedance.com Signed-off-by: Muchun Song Signed-off-by: Andrew Morton Cc: David Hildenbrand Cc: Oscar Salvador Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Jonathan Corbet Cc: Lorenzo Stoakes Cc: Mike Rapoport Cc: Qi Zheng Cc: Nicholas Piggin Cc: Christophe Leroy Cc: Ritesh Harjani (IBM) Cc: Shrikanth Hegde Cc: Randy Dunlap Cc: Lance Yang --- include/linux/mmzone.h | 7 +------ mm/sparse-vmemmap.c | 39 +++++++++++++++++++++++++++++++++++---- 2 files changed, 36 insertions(+), 10 deletions(-) --- a/include/linux/mmzone.h~mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically +++ a/include/linux/mmzone.h @@ -113,11 +113,6 @@ (VMEMMAP_OPTIMIZATION_PAGES * PAGE_SIZE / sizeof(struct page)) #define VMEMMAP_OPTIMIZATION_MIN_ORDER (ilog2(VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) + 1) -#define __VMEMMAP_OPTIMIZATION_NR_ORDERS \ - (MAX_FOLIO_ORDER - VMEMMAP_OPTIMIZATION_MIN_ORDER + 1) -#define VMEMMAP_OPTIMIZATION_NR_ORDERS \ - (__VMEMMAP_OPTIMIZATION_NR_ORDERS > 0 ? __VMEMMAP_OPTIMIZATION_NR_ORDERS : 0) - enum migratetype { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, @@ -1156,7 +1151,7 @@ struct zone { atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS]; atomic_long_t vm_numa_event[NR_VM_NUMA_EVENT_ITEMS]; #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP - struct page *vmemmap_tails[VMEMMAP_OPTIMIZATION_NR_ORDERS]; + struct page **vmemmap_tails; #endif } ____cacheline_internodealigned_in_smp; --- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically +++ a/mm/sparse-vmemmap.c @@ -170,16 +170,47 @@ static void * __meminit vmemmap_alloc_bl } #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP +#define VMEMMAP_OPTIMIZATION_NR_ORDERS (MAX_FOLIO_ORDER - VMEMMAP_OPTIMIZATION_MIN_ORDER + 1) + +static __ref struct page **vmemmap_tails(struct zone *zone) +{ + const size_t size = array_size(VMEMMAP_OPTIMIZATION_NR_ORDERS, + sizeof(*zone->vmemmap_tails)); + struct page **pages = READ_ONCE(zone->vmemmap_tails); + + if (pages) + return pages; + + pages = slab_is_available() ? kzalloc_objs(*pages, VMEMMAP_OPTIMIZATION_NR_ORDERS) : + memblock_alloc(size, __alignof__(*pages)); + if (!pages) + return NULL; + + if (cmpxchg(&zone->vmemmap_tails, NULL, pages) != NULL) { + if (slab_is_available()) + kfree(pages); + else + memblock_free(pages, size); + pages = READ_ONCE(zone->vmemmap_tails); + } + + return pages; +} + struct page __ref *vmemmap_shared_tail_page(unsigned int order, struct zone *zone) { const unsigned int idx = order - VMEMMAP_OPTIMIZATION_MIN_ORDER; - struct page *page; + struct page *page, **pages; void *addr; if (WARN_ON_ONCE(idx >= VMEMMAP_OPTIMIZATION_NR_ORDERS)) return NULL; - page = READ_ONCE(zone->vmemmap_tails[idx]); + pages = vmemmap_tails(zone); + if (!pages) + return NULL; + + page = READ_ONCE(pages[idx]); if (page) return page; @@ -194,12 +225,12 @@ struct page __ref *vmemmap_shared_tail_p } page = virt_to_page(addr); - if (cmpxchg(&zone->vmemmap_tails[idx], NULL, page) != NULL) { + if (cmpxchg(&pages[idx], NULL, page) != NULL) { if (slab_is_available()) __free_page(page); else memblock_free(addr, PAGE_SIZE); - page = READ_ONCE(zone->vmemmap_tails[idx]); + page = READ_ONCE(pages[idx]); } return page; _ Patches currently in -mm which might be from muchun.song@linux.dev are mm-sparse-vmemmap-factor-out-shared-vmemmap-tail-page-allocation.patch mm-sparse-vmemmap-allocate-shared-tail-page-array-dynamically.patch mm-sparse-vmemmap-introduce-config_vmemmap_optimization.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-switch-device-dax-to-shared-tail-vmemmap-pages-fix.patch mm-sparse-vmemmap-move-vmemmap-optimization-helpers-to-a-public-header.patch powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages-fix.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 mm-sparse-vmemmap-drop-vmemmap_populate_dax.patch mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch mm-sparse-vmemmap-remove-the-unused-ptpfn-argument.patch mm-sparse-vmemmap-open-code-vmemmap_populate_address.patch mm-mm_init-add-zone-mismatch-warning-during-page-init.patch