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[2003:d8:2f14:2400:afc:9797:137c:a25b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e2a998314sm29241655e9.3.2025.09.24.02.50.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 02:51:00 -0700 (PDT) Message-ID: Date: Wed, 24 Sep 2025 11:50:58 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 2/2] mm: add PMD-level huge page support for remap_pfn_range() To: Yin Tirui , akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, catalin.marinas@arm.com, will@kernel.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, anshuman.khandual@arm.com, yangyicong@hisilicon.com, ardb@kernel.org, willy@infradead.org, apopple@nvidia.com, samuel.holland@sifive.com, luxu.kernel@bytedance.com, abrestic@rivosinc.com, yongxuan.wang@sifive.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org Cc: wangkefeng.wang@huawei.com, chenjun102@huawei.com References: <20250923133104.926672-1-yintirui@huawei.com> <20250923133104.926672-3-yintirui@huawei.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 23.09.25 15:31, Yin Tirui wrote: > Add PMD-level huge page support to remap_pfn_range(), automatically > creating huge mappings when prerequisites are satisfied (size, alignment, > architecture support, etc.) and falling back to normal page mappings > otherwise. > > Implement special huge PMD splitting by utilizing the pgtable deposit/ > withdraw mechanism. When splitting is needed, the deposited pgtable is > withdrawn and populated with individual PTEs created from the original > huge mapping, using pte_clrhuge() to clear huge page attributes. > > Update arch_needs_pgtable_deposit() to return true when PMD pfnmap > support is enabled, ensuring proper pgtable management for huge > pfnmap operations. > > Introduce pfnmap_max_page_shift parameter to control maximum page > size and "nohugepfnmap" boot option to disable huge pfnmap entirely. Why? If an arch supports it we should just do it. Or what's the reason behind that? > > Signed-off-by: Yin Tirui > --- > include/linux/pgtable.h | 6 +++- > mm/huge_memory.c | 22 ++++++++---- > mm/memory.c | 74 ++++++++++++++++++++++++++++++++++++----- > 3 files changed, 85 insertions(+), 17 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 4c035637eeb7..4028318552ca 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1025,7 +1025,11 @@ extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp); > #endif > > #ifndef arch_needs_pgtable_deposit > -#define arch_needs_pgtable_deposit() (false) > +#define arch_needs_pgtable_deposit arch_needs_pgtable_deposit > +static inline bool arch_needs_pgtable_deposit(void) > +{ > + return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP); > +} > #endif > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 9c38a95e9f09..9f20adcbbb55 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2857,14 +2857,22 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > if (!vma_is_anonymous(vma)) { > old_pmd = pmdp_huge_clear_flush(vma, haddr, pmd); > - /* > - * We are going to unmap this huge page. So > - * just go ahead and zap it > - */ > - if (arch_needs_pgtable_deposit()) > - zap_deposited_table(mm, pmd); Are you sure we can just entirely remove this block for !vma_is_anonymous(vma)? -- Cheers David / dhildenb