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 D5A8C3C98BA for ; Sat, 10 Oct 2026 20:43:11 +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=1791664993; cv=none; b=ss3LM4T3s8vxwzOX0v9+bpbtYuF/opw7+EVrpwmZnaZahkVabomIXKPXv7V87yyj4A5gjGEJ/sJgrkjMuHTQTa9LUrjTtV1g8+cP/gA0pXNcR5jTTFvtFmHfXiOCOwd8jz+prvzxFSsY+8IpPT08u8A5LEEM0KWC6BqrWmGsaSI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791664993; c=relaxed/simple; bh=gMH+VwpvEUH+3hnvBcs9F1EgNaXpFmbmVbctJQ47pcM=; h=Date:To:From:Subject:Message-Id; b=UBCIgb6AKKpP8EEkSqteWswjSwK9iaK4cVUxAIrx40Qjtsf/vJK5atLUXsMTFaHN+fogmGlX90I9rd+10Y1/K+lgaBdwh7ScBX36ZCXz7ZGELxDFkoubnxPwJ4r7ujfpaP51h0o82eCBSejWHbW8bWZR320Jm4EUhoAFcA/fBmg= 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=jzFApioJ; 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="jzFApioJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 688A91F00893; Sat, 10 Oct 2026 20:43:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1791664991; bh=vT2jaG5ws+0qihZvFs5LYRT0ae1KWguwbASFSHMN0D8=; h=Date:To:From:Subject; b=jzFApioJu1TlWpckfDjKRmhtLDlXHyvSjbuj43MCtHmwiFEdS5lO6V2f7bKoQpmxz HJsfxcx6yJSary79r/nBgOsqukZvEM4HoUCXQavaQlYS+qe7lVxd+tMVrd0n9kkbaW +C3yvqCZr/ySDfQzaAWHXTLu27+/HydjDuSOrNtI= Date: Sat, 10 Oct 2026 13:43:11 -0700 To: mm-commits@vger.kernel.org,muchun.song@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch added to mm-unstable branch Message-Id: <20261010204311.688A91F00893@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: support device DAX in common vmemmap path has been added to the -mm mm-unstable branch. Its filename is mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.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-support-device-dax-in-common-vmemmap-path.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: support device DAX in common vmemmap path Date: Sat, 10 Oct 2026 15:57:51 +0800 The common vmemmap population path cannot yet handle optimized Device DAX mappings on its own. It uses pfn_to_zone() to find the shared tail page, but Device DAX populates its vmemmap at runtime before the ZONE_DEVICE span is initialized. Teach the common path to use device_zone() for runtime optimized vmemmap population while retaining pfn_to_zone() for early boot. This allows the same path to support both early boot mappings and Device DAX. The backing PFN supplied by the Device DAX-specific population path is no longer used, allowing the redundant lookup and population code to be removed later. Link: https://lore.kernel.org/20261010075755.83339-3-songmuchun@bytedance.com Signed-off-by: Muchun Song Signed-off-by: Andrew Morton Reviewed-by: Lance Yang Acked-by: Qi Zheng Cc: Madhavan Srinivasan Cc: Mike Rapoport Cc: David Hildenbrand Cc: Michael Ellerman Cc: Nicholas Piggin Cc: Christophe Leroy Cc: Ritesh Harjani (IBM) Cc: Shrikanth Hegde Cc: Lorenzo Stoakes Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Suren Baghdasaryan Cc: Michal Hocko --- mm/sparse-vmemmap.c | 62 +++++++++++++++++++++++------------------- 1 file changed, 34 insertions(+), 28 deletions(-) --- a/mm/sparse-vmemmap.c~mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path +++ a/mm/sparse-vmemmap.c @@ -241,18 +241,43 @@ static __meminit void *vmemmap_alloc_pte struct page *page; const unsigned int order = pfn_to_section_compound_order(pfn); - /* - * Device DAX still relies on vmemmap_populate_compound_pages() for - * head/first-tail allocation and tail-page reuse. - */ if (!vmemmap_optimizable_pfn(pfn)) return vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap); - zone = pfn_to_zone(pfn, node); + /* + * Before slab is available, vmemmap optimization is used for early + * system RAM, whose zone can be determined from the PFN. + * + * Once slab is available, only ZONE_DEVICE memory reaches this + * optimized population path. Its zone span has not been initialized + * while its vmemmap is being populated, so pfn_to_zone() cannot be + * used. Obtain ZONE_DEVICE directly from the node instead. + */ + zone = slab_is_available() ? device_zone(node) : pfn_to_zone(pfn, node); page = vmemmap_shared_tail_page(order, zone); if (!page) return NULL; + /* + * During early vmemmap population, the shared tail vmemmap backing + * page is allocated from memblock before its struct page can safely + * participate in page refcounting. Therefore, no reference can be + * held for each shared PTE mapping, and the mappings must be unshared + * before the vmemmap is depopulated. + * + * Once slab is available, the shared backing page is allocated from + * the buddy allocator and can be refcounted. Hold one reference for + * each shared PTE mapping. The architecture vmemmap teardown drops + * the reference through __free_pages() when removing the mapping, + * preventing the backing page from being freed while it is shared. + * + * The backing page may be shared by enough PTE mappings to exhaust + * the positive range of its reference count. Stop populating the + * vmemmap if another reference cannot be acquired. + */ + if (slab_is_available() && !try_get_page(page)) + return NULL; + return page_address(page); } @@ -264,31 +289,12 @@ static pte_t * __meminit vmemmap_pte_pop if (pte_none(ptep_get(pte))) { pte_t entry; + void *p = vmemmap_alloc_pte(pfn, node, altmap); - if (ptpfn == (unsigned long)-1) { - void *p = vmemmap_alloc_pte(pfn, node, altmap); + if (!p) + return NULL; - if (!p) - return NULL; - ptpfn = PHYS_PFN(__pa(p)); - } else { - /* - * When a PTE/PMD entry is freed from the init_mm - * there's a free_pages() call to this page allocated - * 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. - */ - if (slab_is_available() && - !try_get_page(pfn_to_page(ptpfn))) - return NULL; - } - entry = pfn_pte(ptpfn, PAGE_KERNEL); + entry = pfn_pte(PHYS_PFN(__pa(p)), PAGE_KERNEL); set_pte_at(&init_mm, addr, pte, entry); } else if (WARN_ON_ONCE(vmemmap_optimizable_pfn(pfn))) return NULL; _ 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 mm-mm_init-add-zone-mismatch-warning-during-page-init-fix.patch mm-fix-missing-page-table-destructor-in-pagetable_free.patch riscv-mm-fix-hotplug-page-table-destructor-handling.patch riscv-mm-fix-missing-destructor-for-hotplug-pud-tables.patch arm64-mm-fix-destructor-for-unconstructed-hotplug-page-tables.patch