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[2003:cb:c718:100:347d:db94:161d:398f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4396180f7d6sm17145955e9.17.2025.02.13.04.59.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2025 04:59:27 -0800 (PST) Message-ID: <9bc91fe3-c590-48e2-b29f-736d0b056c34@redhat.com> Date: Thu, 13 Feb 2025 13:59:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6] arm64: mm: Populate vmemmap/linear at the page level for hotplugged sections To: Zhenhua Huang , anshuman.khandual@arm.com, catalin.marinas@arm.com Cc: will@kernel.org, ardb@kernel.org, ryan.roberts@arm.com, mark.rutland@arm.com, joey.gouly@arm.com, dave.hansen@linux.intel.com, akpm@linux-foundation.org, chenfeiyang@loongson.cn, chenhuacai@kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, quic_tingweiz@quicinc.com, stable@vger.kernel.org References: <20250213075703.1270713-1-quic_zhenhuah@quicinc.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C469B160004 X-Stat-Signature: sbe8ss9eh7jwubn7x4xu6fbq7hs9zu8z X-HE-Tag: 1739451572-255066 X-HE-Meta: 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 mzF+LSkp 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 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 13.02.25 08:57, Zhenhua Huang wrote: > On the arm64 platform with 4K base page config, SECTION_SIZE_BITS is set > to 27, making one section 128M. The related page struct which vmemmap > points to is 2M then. > Commit c1cc1552616d ("arm64: MMU initialisation") optimizes the > vmemmap to populate at the PMD section level which was suitable > initially since hot plug granule is always one section(128M). However, > commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > introduced a 2M(SUBSECTION_SIZE) hot plug granule, which disrupted the > existing arm64 assumptions. > > Considering the vmemmap_free -> unmap_hotplug_pmd_range path, when > pmd_sect() is true, the entire PMD section is cleared, even if there is > other effective subsection. For example page_struct_map1 and > page_strcut_map2 are part of a single PMD entry and they are hot-added > sequentially. Then page_struct_map1 is removed, vmemmap_free() will clear > the entire PMD entry freeing the struct page map for the whole section, > even though page_struct_map2 is still active. Similar problem exists > with linear mapping as well, for 16K base page(PMD size = 32M) or 64K > base page(PMD = 512M), their block mappings exceed SUBSECTION_SIZE. > Tearing down the entire PMD mapping too will leave other subsections > unmapped in the linear mapping. > > To address the issue, we need to prevent PMD/PUD/CONT mappings for both > linear and vmemmap for non-boot sections if corresponding size on the > given base page exceeds SUBSECTION_SIZE(2MB now). > > Cc: # v5.4+ > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > Reviewed-by: Catalin Marinas > Signed-off-by: Zhenhua Huang Just so I understand correctly: for ordinary memory-sections-size hotplug (NVDIMM, virtio-mem), we still get a large mapping where possible? -- Cheers, David / dhildenb