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b=Grj63EomMmOFpWGNtNOisS3ON2mRVEMypsHP3ZZRNfWxdN61pkoauFTDOjgQFK62T eVxgpKP6dJISPZQvvWkHjQjDrqp69WceyTkNA5XrrQS50WllfO+zpfgoFWdMOtZuWb d5R/t1WHiQDDneBjPc9UbC4gnlkI2KYlcHF4WA631f8AsuQLZJ6HxJQm+8GiTIzHHb 5amDF0CEQLBDkIgdXW+xtT3ivF4XOvfTRKRCyLBbhSTR/49/vPbD3EmPEzu8cWK4pr 8yuR0p6ti1+jWnCDofwE/zlRGcdP2GUvWSIBzKnvVcEZyZlykkkTz+EO8c2NU9AaIy 7x0EbKwjy/qzA== Message-ID: <36a93f95-2fb4-4310-bef2-88c12dbe7971@kernel.org> Date: Tue, 29 Sep 2026 09:21:28 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 02/12] mm/sparse-vmemmap: allocate shared tail page array dynamically To: Muchun Song , Andrew Morton , Oscar Salvador , Madhavan Srinivasan , Michael Ellerman , Jonathan Corbet Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, Muchun Song , Lorenzo Stoakes , Mike Rapoport , Qi Zheng , Nicholas Piggin , Christophe Leroy , Randy Dunlap , Lance Yang References: <20260927025441.741633-1-songmuchun@bytedance.com> <20260927025441.741633-3-songmuchun@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 1D06040005 X-Rspam-User: X-Stat-Signature: n6m9aime1hpj77n6p6pas7cm8fj3qd78 X-HE-Tag: 1790666494-973145 X-HE-Meta: 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 j9LmeAo1 0B8L/5ZR9qsZZcY9qHy7jJ49G+NxVDCUjYyomGWbULZVk3snjiac40oRCrXp6in2a74rMkP/R4HaxgUTaRWUfa2wP3h8C0aJnowuLrmdk+a553PuQOKwymK9eTmX8FSeDlOm0qTyXmSoe3tJsOAyP3fP3zJ1lzyEzbRXR/VcRy5VgHE1VJqrWepAVZuY+5Os4dvBazkx0bkCYbNj1L9SP2avzPVoKonIBEEEQrGG/QyzwVe8pEQffAPUqFrMEcGAmpp3FVozISf8GzKJyBJYWi5D8yXqMQN1uLP/q Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/27/26 04:54, Muchun Song wrote: > 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. > > Signed-off-by: Muchun Song > --- > v5: > - Add this patch to fix the RISC-V build failure under the configuration > reported by the kernel test robot > --- > include/linux/mmzone.h | 7 +------ > mm/sparse-vmemmap.c | 35 +++++++++++++++++++++++++++++++---- > 2 files changed, 32 insertions(+), 10 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index acd94cecc0d3..68807ff7f946 100644 > --- a/include/linux/mmzone.h > +++ b/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; > [...] > struct page __ref *vmemmap_shared_tail_page(unsigned int order, struct zone *zone) > { > void *addr; > - struct page *page; > + struct page *page, **pages; > const unsigned int idx = order - VMEMMAP_OPTIMIZATION_MIN_ORDER; > > if (WARN_ON_ONCE(idx >= VMEMMAP_OPTIMIZATION_NR_ORDERS)) > return NULL; > > - page = READ_ONCE(zone->vmemmap_tails[idx]); > + pages = READ_ONCE(zone->vmemmap_tails) ? : vmemmap_tails_alloc(zone); This reads much nicer if you handle the READ_ONCE(zone->vmemmap_tails) inside the function. pages = vmemmap_tails(zone); So just place the entire logic of obtaining the array in there. Apart from that LGTM. -- Cheers, David