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b=AEzNcPowN4BXmt/D6Aou5d8c+1I3HBIPjz0gA7sikgv0Ip1rzk5T6BtqxHkZb5VkE DePut29gHzvT8VyvfG9xbgwY+Kibkxt4Pb5EjnOaeBTV5BMNyVVVLMFUNjpBMd1Ugk mPQBR5np1zulD6HftFxxFg09JX0BLr6DopqBYv2cA87ylu0Mt8qe60WVBtaHupSjIe bLmBOpbkINgrjrAieAMtg9kVh9w4PfCG4/U4g6dxJUvV67RnqoDmVI4M9E6VV8PHBh Kt0gJ+sj6BjoBSDBo0z+ZQb2tH1OkHtkHK+Ki2AyawzNqqsCg9diht8nNeNd/ZXMSg GTBttbb6q2jYQ== Message-ID: <062900fa-6419-4748-81d1-9128ce6c46d0@kernel.org> Date: Thu, 5 Feb 2026 13:56:36 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 06/17] LoongArch/mm: Align vmemmap to maximal folio size From: "David Hildenbrand (Arm)" To: Kiryl Shutsemau , Andrew Morton , Muchun Song , Matthew Wilcox , Usama Arif , Frank van der Linden Cc: Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , Huacai Chen , WANG Xuerui , Palmer Dabbelt , Paul Walmsley , Albert Ou , Alexandre Ghiti , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org References: <20260202155634.650837-1-kas@kernel.org> <20260202155634.650837-7-kas@kernel.org> <2ce0e684-de54-43ec-be7d-c58bbffb3f4e@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3093A18000E X-Stat-Signature: yxgk9h6guxi9d34cfdemtmmzrx8wmhq7 X-Rspam-User: X-HE-Tag: 1770296205-859903 X-HE-Meta: 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 7zhNFthx 9sCase84mmZI/qcDzPC6GZwmzi3+U1OJzcq0fp1aMvZULrMOJrLtXEXoQHt3ofRD9Dh4VGLh/oppbuF/tbv2XTlTjBrbFa+gzDW+PiYnDk8/iN1dMn3454W279E6FAgKmq10WOcXPoa0kMPDK1Uskw5QK2XGhK7Ys7OeOuSFQLGhEjR97a+IU5xcswyTDMXYEKeXBQS82LkYcy3cSj3UfKBqrpRIxqUS1qujXoL+sENjg81u2VbcCJOem+W79ZSdUFmhXB6MTGZthwh+Rg5JTillDP1VLv4nvXmotHXPJOOB9TFUkoYLVDNgmhQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/4/26 17:56, David Hildenbrand (arm) wrote: > On 2/2/26 16:56, Kiryl Shutsemau wrote: >> The upcoming change to the HugeTLB vmemmap optimization (HVO) requires >> struct pages of the head page to be naturally aligned with regard to the >> folio size. >> >> Align vmemmap to MAX_FOLIO_NR_PAGES. >> >> Signed-off-by: Kiryl Shutsemau >> --- >>   arch/loongarch/include/asm/pgtable.h | 3 ++- >>   1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/ >> include/asm/pgtable.h >> index c33b3bcb733e..f9416acb9156 100644 >> --- a/arch/loongarch/include/asm/pgtable.h >> +++ b/arch/loongarch/include/asm/pgtable.h >> @@ -113,7 +113,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / >> sizeof(unsigned long)]; >>        min(PTRS_PER_PGD * PTRS_PER_PUD * PTRS_PER_PMD * PTRS_PER_PTE * >> PAGE_SIZE, (1UL << cpu_vabits) / 2) - PMD_SIZE - VMEMMAP_SIZE - >> KFENCE_AREA_SIZE) >>   #endif >> -#define vmemmap        ((struct page *)((VMALLOC_END + PMD_SIZE) & >> PMD_MASK)) >> +#define VMEMMAP_ALIGN    max(PMD_SIZE, MAX_FOLIO_NR_PAGES * >> sizeof(struct page)) >> +#define vmemmap        ((struct page *)(ALIGN(VMALLOC_END, >> VMEMMAP_ALIGN))) > > > Same comment, the "MAX_FOLIO_NR_PAGES * sizeof(struct page)" is just > black magic here > and the description of the situation is wrong. > > Maybe you want to pull the magic "MAX_FOLIO_NR_PAGES * sizeof(struct > page)" into the core and call it > > #define MAX_FOLIO_VMEMMAP_ALIGN    (MAX_FOLIO_NR_PAGES * sizeof(struct > page)) > > But then special case it base on (a) HVO being configured in an (b) HVO > being possible > > #ifdef HUGETLB_PAGE_OPTIMIZE_VMEMMAP && is_power_of_2(sizeof(struct page) > /* A very helpful comment explaining the situation. */ > #define MAX_FOLIO_VMEMMAP_ALIGN    (MAX_FOLIO_NR_PAGES * sizeof(struct > page)) > #else > #define MAX_FOLIO_VMEMMAP_ALIGN    0 > #endif > > Something like that. > Thinking about this ... the vmemmap start is always struct-page-aligned. Otherwise we'd be in trouble already. Isn't it then sufficient to just align the start to MAX_FOLIO_NR_PAGES? Let's assume sizeof(struct page) == 64 and MAX_FOLIO_NR_PAGES = 512 for simplicity. vmemmap start would be multiples of 512 (0x0010000000). 512, 1024, 1536, 2048 ... Assume we have an 256-pages folio at 1536+256 = 0x111000000 Assume we have the last page of that folio (0x011111111111), we would just get to the start of that folio by AND-ing with ~(256-1). Which case am I ignoring? -- Cheers, David