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 76A4B447815 for ; Fri, 24 Jul 2026 16:45:12 +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=1784911515; cv=none; b=KIyLjxuiHKBeNSdsuavDL+QR4y3eOBX+LPigo7wF4v6ymRLyl+gRttttGC0btTJyH7cpT6uA8a+IzYT5hsr+ZzbMEuezsT1VkiwoaPDNzZlrIb0JyV84CED0Qit+0phf2TQk4gD/+UnVRsKesiuCFHDf9uTiEpaSGZOHIqMpLaw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784911515; c=relaxed/simple; bh=bF3e5D2yrXOnLWYpHuyaPKvJKFZw9WcMqL2VVQXlulY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LZkc3YIK1k3uiasq6renof/5rt44c3tEBzh+IFa9uw8DX2AQMXtNMWEaBrjwVDcs1jLsF2QDLyRwMHQhksLywj5uSLtMNJviqwD3kqQiLoZir39o16f3IzI5tzq4WeOv/KoxNnB19H1oeODbcmtoICmHaB8frYeYTdxTK3qIVvg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eZEFSwPf; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eZEFSwPf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E27CD1F00A3E; Fri, 24 Jul 2026 16:45:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784911510; bh=xhOyLx/3KNCyR3I+7OpRPN49qhTOhZ32ASfTkV/dML8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=eZEFSwPffETyu68sUX51mU3gLoscRP3Wa4iyZfiYCgxR+Pq+pbttUdF8nWsI/lUrY X1jYAN4qAjwPxQ2AhJogZJ6qL8lwLVRd8q1pbC8Nw+JFj51CcaNBFkitNfGzfZbRIs usnQHx81g3JLtN/q4DBYigUfV8Hrpht+Kr2M20TU7tf9fI9WC7U8OpXIVOUe4BAhGd 2HrREPDdvc+4VamZOWmyligGHvLyAPju1A+9UmBl+IWQDDQYfj1mBKhJAHDnsikZJK sbfmImxt9/uohj0nhHVZ0GlThaByiizKWygsYceU0dlRtc5JFt2o2KPWEjtFvEjZxG 1P+qppv4YiuQg== From: Sasha Levin To: stable@vger.kernel.org Cc: Muchun Song , "Mike Rapoport (Microsoft)" , Oscar Salvador , "David Hildenbrand (Arm)" , "Liam R. Howlett" , "Aneesh Kumar K.V" , Joao Martins , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Nicholas Piggin , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton , Sasha Levin Subject: [PATCH 6.18.y 2/2] mm/sparse-vmemmap: fix DAX vmemmap accounting with optimization Date: Fri, 24 Jul 2026 12:45:05 -0400 Message-ID: <20260724164505.471020-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260724164505.471020-1-sashal@kernel.org> References: <2026072034-plow-sliceable-b741@gregkh> <20260724164505.471020-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Muchun Song [ Upstream commit 721a73e30c9e3e8fcffe1725bcede1bbd20b4918 ] When vmemmap optimization is enabled for DAX, the nr_memmap_pages counter in /proc/vmstat is incorrect. The current code always accounts for the full, non-optimized vmemmap size, but vmemmap optimization reduces the actual number of vmemmap pages by reusing tail pages. This causes the system to overcount vmemmap usage, leading to inaccurate page statistics in /proc/vmstat. Fix this by introducing section_nr_vmemmap_pages(), which returns the exact vmemmap page count for a given pfn range based on whether optimization is in effect. Link: https://lore.kernel.org/20260428081855.1249045-5-songmuchun@bytedance.com Fixes: 15995a352474 ("mm: report per-page metadata information") Signed-off-by: Muchun Song Acked-by: Mike Rapoport (Microsoft) Acked-by: Oscar Salvador Acked-by: David Hildenbrand (Arm) Acked-by: Liam R. Howlett Cc: "Aneesh Kumar K.V" Cc: Joao Martins Cc: Lorenzo Stoakes Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Michal Hocko Cc: Nicholas Piggin Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/sparse-vmemmap.c | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c index 2c9fbc07c95697..ecd780cb5bfc58 100644 --- a/mm/sparse-vmemmap.c +++ b/mm/sparse-vmemmap.c @@ -679,6 +679,31 @@ void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn) } } +static int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages, + struct vmem_altmap *altmap, struct dev_pagemap *pgmap) +{ + const unsigned int order = pgmap ? pgmap->vmemmap_shift : 0; + const unsigned long pages_per_compound = 1UL << order; + + VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, PAGES_PER_SUBSECTION)); + VM_WARN_ON_ONCE(nr_pages > PAGES_PER_SECTION); + + if (!vmemmap_can_optimize(altmap, pgmap)) + return DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE); + + if (order < PFN_SECTION_SHIFT) { + VM_WARN_ON_ONCE(!IS_ALIGNED(pfn | nr_pages, pages_per_compound)); + return VMEMMAP_RESERVE_NR * 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_RESERVE_NR; + + return 0; +} + static struct page * __meminit populate_section_memmap(unsigned long pfn, unsigned long nr_pages, int nid, struct vmem_altmap *altmap, struct dev_pagemap *pgmap) @@ -686,7 +711,7 @@ static struct page * __meminit populate_section_memmap(unsigned long pfn, struct page *page = __populate_section_memmap(pfn, nr_pages, nid, altmap, pgmap); - memmap_pages_add(DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE)); + memmap_pages_add(section_nr_vmemmap_pages(pfn, nr_pages, altmap, pgmap)); return page; } @@ -697,7 +722,7 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages, unsigned long start = (unsigned long) pfn_to_page(pfn); unsigned long end = start + nr_pages * sizeof(struct page); - memmap_pages_add(-1L * (DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE))); + memmap_pages_add(-section_nr_vmemmap_pages(pfn, nr_pages, altmap, pgmap)); vmemmap_free(start, end, altmap); } @@ -705,9 +730,10 @@ static void free_map_bootmem(struct page *memmap) { unsigned long start = (unsigned long)memmap; unsigned long end = (unsigned long)(memmap + PAGES_PER_SECTION); + unsigned long pfn = page_to_pfn(memmap); - memmap_boot_pages_add(-1L * (DIV_ROUND_UP(PAGES_PER_SECTION * sizeof(struct page), - PAGE_SIZE))); + memmap_boot_pages_add(-section_nr_vmemmap_pages(pfn, PAGES_PER_SECTION, + NULL, NULL)); vmemmap_free(start, end, NULL); } -- 2.53.0