From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 5E4C21A6823 for ; Thu, 6 Aug 2026 03:04:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785985489; cv=none; b=faEBFoq7UDWDyVfeccQbjJpTaS/U7G2fgk9JopWeWKpdpQhkCcnRTTNkRmtupxGAiT6IhS+Geza9uHOW4mFuHUWk38/AAL9VklCUzp33PuTQ+mLYRipmhRrZKkHUQrRSSXdSclIW5yNmWWm2AkSi6wko4j9buqj4mgTDgr9UYrg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785985489; c=relaxed/simple; bh=27QZcyc+fjdT/e9Nb0afKHxmCuB5OnG8/0Hny//Wxak=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=APwNQ4Pv3ZfEwww8eBTNS3tn1VQUIoEpdoA+V6JsFvYgs80/sikkJHot0G1qII92ZbzQ6ziaoNmTdz0VAeXu6vIi+NqxgM9CycjGsL9trPHDLbpqetEWhvSxchqBHtKYlZLubKXsa/NCtHLq9L9vrGImqtP0rcaksNCdjhIFVEc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ImvMNWEs; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ImvMNWEs" Message-ID: <978060e0-a202-43b2-b84d-b1950b2d28c1@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1785985483; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PeFhF0M/SpcuVTAHQU+II4MEXYOvkh6h/IJxQ8sqVSw=; b=ImvMNWEstqKdQmDiFyQsqTUlMnWbcUta+OkPhlvxqCD+SYalu73/Onx13vnKMC8bh4lRLN XTnBHwGoWSFTRhTdiLxOjgynzrMfVXuciNDCyVl4OQbDjmnaii4lRyYodZex+Oa/wojb2j eD+eU36NpVL08kXcswYlYOHBxe+cv84= Date: Thu, 6 Aug 2026 11:04:35 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3 08/17] mm/sparse-vmemmap: support section-based vmemmap optimization To: Muchun Song Cc: Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Michal Hocko , David Laight , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Oscar Salvador , David Hildenbrand References: <20260804035535.2846016-1-songmuchun@bytedance.com> <20260804035535.2846016-9-songmuchun@bytedance.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20260804035535.2846016-9-songmuchun@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2026/8/4 11:55, Muchun Song wrote: > Teach sparse-vmemmap population code to use the compound page order > when deciding whether a vmemmap page can be optimized. > > With this information, the common sparse-vmemmap population path can > allocate or reuse shared tail vmemmap pages directly instead of relying > on HugeTLB-specific handling. > > This centralizes vmemmap optimization logic in the sparse-vmemmap code, > based on section metadata, and prepares for sharing the same mechanism > across different users of vmemmap optimization, including HugeTLB and > DAX. > > Signed-off-by: Muchun Song > --- > v2: > - Keep vmemmap accounting and population logic in sparse-vmemmap.c > (suggested by Mike Rapoport) > - Move vmemmap_get_tail() before its first use instead of adding only a > forward declaration in the previous patch (suggested by Mike Rapoport) > - Simplify the PMD path handling for HVO-covered sections > --- > mm/sparse-vmemmap.c | 36 ++++++++++++++++++++++++++++++------ > mm/sparse.c | 4 ++-- > mm/sparse.h | 7 +++++++ > 3 files changed, 39 insertions(+), 8 deletions(-) > > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c > index b770fe2428fd..b69a7af76858 100644 > --- a/mm/sparse-vmemmap.c > +++ b/mm/sparse-vmemmap.c > @@ -186,6 +186,11 @@ static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone * > > return tail; > } > +#else > +static inline struct page *vmemmap_get_tail(unsigned int order, struct zone *zone) > +{ > + return NULL; > +} > #endif > > static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node, > @@ -193,12 +198,24 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in > unsigned long ptpfn, unsigned long flags) > { > pte_t *pte = pte_offset_kernel(pmd, addr); > + unsigned long pfn = page_to_pfn((struct page *)addr); > + > if (pte_none(ptep_get(pte))) { > pte_t entry; > - void *p; > + > + if (pfn_vmemmap_optimizable(pfn) && ptpfn == (unsigned long)-1) { > + unsigned int order = pfn_to_section_order(pfn); > + struct zone *zone = pfn_to_zone(pfn, node); > + struct page *page = vmemmap_get_tail(order, zone); > + > + if (!page) > + return NULL; > + ptpfn = page_to_pfn(page); > + } > > if (ptpfn == (unsigned long)-1) { > - p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap); > + void *p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap); > + > if (!p) > return NULL; > ptpfn = PHYS_PFN(__pa(p)); > @@ -217,7 +234,8 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in > } > entry = pfn_pte(ptpfn, PAGE_KERNEL); > set_pte_at(&init_mm, addr, pte, entry); > - } > + } else if (WARN_ON_ONCE(pfn_vmemmap_optimizable(pfn))) > + return NULL; > return pte; > } > > @@ -406,6 +424,9 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end, > pmd_t *pmd; > > for (addr = start; addr < end; addr = next) { > + unsigned long pfn = page_to_pfn((struct page *)addr); > + const struct mem_section *ms = __pfn_to_section(pfn); > + > next = pmd_addr_end(addr, end); > > pgd = vmemmap_pgd_populate(addr, node); > @@ -421,7 +442,7 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end, > return -ENOMEM; > > pmd = pmd_offset(pud, addr); > - if (pmd_none(pmdp_get(pmd))) { > + if (pmd_none(pmdp_get(pmd)) && !section_vmemmap_optimizable(ms)) { > void *p; > > p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap); > @@ -439,8 +460,11 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end, > */ > return -ENOMEM; > } > - } else if (vmemmap_check_pmd(pmd, node, addr, next)) > + } else if (vmemmap_check_pmd(pmd, node, addr, next)) { > + if (WARN_ON_ONCE(section_vmemmap_optimizable(ms))) > + return -ENOTSUPP; > continue; > + } > if (vmemmap_populate_basepages(addr, next, node, altmap)) > return -ENOMEM; > } > @@ -648,7 +672,7 @@ 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, > +int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages, The kernel test robot reported a compilation issue: when CONFIG_MEMORY_HOTPLUG = n && CONFIG_SPARSEMEM_VMEMMAP=y, section_nr_vmemmap_pages is undefined. This problem is easy to fix, and I will move the entire function outside the CONFIG_MEMORY_HOTPLUG guard in the next version. Thanks. > struct vmem_altmap *altmap, struct dev_pagemap *pgmap) > { > const struct mem_section *ms = __pfn_to_section(pfn); > diff --git a/mm/sparse.c b/mm/sparse.c > index ca9875f568d3..24555a32a5d9 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -315,8 +315,8 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin, > nid, NULL, NULL); > if (!map) > panic("Failed to allocate memmap for section %lu\n", pnum); > - memmap_boot_pages_add(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)); > sparse_init_early_section(nid, map, pnum, 0); > } > } > diff --git a/mm/sparse.h b/mm/sparse.h > index 6ad190ec48cf..f8f852f9f8a2 100644 > --- a/mm/sparse.h > +++ b/mm/sparse.h > @@ -105,8 +105,15 @@ static inline void sparse_init(void) {} > */ > #ifdef CONFIG_SPARSEMEM_VMEMMAP > void sparse_init_subsection_map(void); > +int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages, > + struct vmem_altmap *altmap, struct dev_pagemap *pgmap); > #else > static inline void sparse_init_subsection_map(void) {} > +static inline int section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages, > + struct vmem_altmap *altmap, struct dev_pagemap *pgmap) > +{ > + return DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE); > +} > #endif /* CONFIG_SPARSEMEM_VMEMMAP */ > > #endif /* __MM_SPARSE_H */