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 9569B40803D for ; Fri, 9 Oct 2026 05:59:01 +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=1791525542; cv=none; b=JXRr3UVZ9UMrppEe2I1XiQ8k0qxK5l7C5DIj9Iwm5t8YORvQ4I1cjq47bODlykm7jlWHCkyf0uJIPd3LLlZ48HXea1CE5g6fxGM3DpYu7M4b2kNOWvVznaEuNYJuzpGTNTtimLNocsl0IePpgxW147YaZm1+AwWJdQZRruPGd6c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791525542; c=relaxed/simple; bh=4HHruWwIbDgjzglyd2yIjZI1fDsc3L4HCfT8HPLDVjA=; h=Date:To:From:Subject:Message-Id; b=VMKXU6RYMCE3OvHtcMFxFxpBKB3ZyvSrNNHQqSP5UtBNj1G6rD/fTX51WbrseHAfQcL2qxmNTCTD0d+bLr9yNomIsHdpRfH7TU1STjeOlB0+0JpCyOdHgjj65Ps5vsEHBsKqu4uJEQynUtFUaFL6tnWeMqCRHUmeLIx3cMGkVd4= 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=oll0xhqi; 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="oll0xhqi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 68B911F000FF; Fri, 9 Oct 2026 05:59:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1791525541; bh=/pxqbAHiF3LGwbE5c/bNbzJBX66LBx10OjoFVh8zWp8=; h=Date:To:From:Subject; b=oll0xhqizl6G2nkF9x0qnTvlrXZpIxsDQeCk3ngJHKvIYi++MQJCsX+Ux+6xVCNHt DW77osFv7u8C3s6UrG6yaihdLIYQrudKfFURZFNyxTdND0Ltm9srzfWhiEfrHVrLgT tb1mGGTDFJzvZUDbp/oUOvUQtZrGRDihr9Tl+RaM= Date: Thu, 08 Oct 2026 22:59:00 -0700 To: mm-commits@vger.kernel.org,sshegde@linux.ibm.com,rppt@kernel.org,ritesh.list@gmail.com,rdunlap@infradead.org,qi.zheng@linux.dev,osalvador@suse.de,npiggin@gmail.com,mpe@ellerman.id.au,maddy@linux.ibm.com,ljs@kernel.org,lance.yang@linux.dev,david@kernel.org,corbet@lwn.net,chleroy@kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch removed from -mm tree Message-Id: <20261009055901.68B911F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: powerpc/mm: switch device DAX to shared tail vmemmap pages has been removed from the -mm tree. Its filename was powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Muchun Song Subject: powerpc/mm: switch device DAX to shared tail vmemmap pages Date: Wed, 30 Sep 2026 22:06:24 +0800 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. [muchun.song@linux.dev: use try_get_page()] Link: https://lore.kernel.org/20260930152826.76084-1-songmuchun@bytedance.com Link: https://lore.kernel.org/20260930140627.57431-10-songmuchun@bytedance.com Signed-off-by: Muchun Song Signed-off-by: Andrew Morton Acked-by: David Hildenbrand (Arm) 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 --- arch/powerpc/mm/book3s64/radix_pgtable.c | 88 +++------------------ include/linux/vmemmap-optimization.h | 6 + mm/sparse-vmemmap.c | 6 - 3 files changed, 21 insertions(+), 79 deletions(-) --- a/arch/powerpc/mm/book3s64/radix_pgtable.c~powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages +++ a/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -19,6 +19,7 @@ #include #include #include +#include #include #include @@ -1041,13 +1042,17 @@ static pte_t * __meminit radix__vmemmap_ /* * When a PTE/PMD entry is freed from the init_mm * there's a free_pages() call to this page allocated - * above. Thus this get_page() is paired with the + * above. Thus this try_get_page() is paired with the * put_page_testzero() on the freeing path. * This can only called by certain ZONE_DEVICE path, * and through vmemmap_populate_compound_pages() when * slab is available. + * + * Use try_get_page() to prevent the shared page refcount + * from overflowing. */ - get_page(reuse); + if (!try_get_page(reuse)) + return NULL; p = page_to_virt(reuse); pr_debug("Tail page reuse vmemmap mapping\n"); } @@ -1250,59 +1255,6 @@ static pte_t * __meminit radix__vmemmap_ 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 +1272,12 @@ int __meminit vmemmap_populate_compound_ 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 +1307,9 @@ int __meminit vmemmap_populate_compound_ 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 +1334,8 @@ int __meminit vmemmap_populate_compound_ 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); --- a/include/linux/vmemmap-optimization.h~powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages +++ a/include/linux/vmemmap-optimization.h @@ -83,6 +83,12 @@ static inline unsigned int pfn_to_sectio { 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) --- a/mm/sparse-vmemmap.c~powerpc-mm-switch-device-dax-to-shared-tail-vmemmap-pages +++ a/mm/sparse-vmemmap.c @@ -240,12 +240,6 @@ struct page __ref *vmemmap_shared_tail_p 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, _ Patches currently in -mm which might be from muchun.song@linux.dev are 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