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[2003:cb:c70f:6900:6c56:80f8:c14:6d2a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a073e5d479sm2116638f8f.92.2025.04.25.04.23.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Apr 2025 04:23:27 -0700 (PDT) Message-ID: <96738f27-25bc-4d9e-9c4e-709e840563eb@redhat.com> Date: Fri, 25 Apr 2025 13:23:26 +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 v2 1/2] mm/huge_memory: Adjust try_to_migrate_one() and split_huge_pmd_locked() To: Zi Yan , Gavin Guo Cc: linux-mm@kvack.org, akpm@linux-foundation.org, gshan@redhat.com, willy@infradead.org, linmiaohe@huawei.com, hughd@google.com, revest@google.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org References: <20250425103859.825879-1-gavinguo@igalia.com> <20250425103859.825879-2-gavinguo@igalia.com> <40B90370-92E1-4E12-979D-7220887CB780@nvidia.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 25.04.25 13:10, Zi Yan wrote: > On 25 Apr 2025, at 6:38, Gavin Guo wrote: > >> The split_huge_pmd_locked function currently performs redundant checks >> for migration entries and folio validation that are already handled by >> the page_vma_mapped_walk mechanism in try_to_migrate_one. >> >> Specifically, page_vma_mapped_walk already ensures that: >> - The folio is properly mapped in the given VMA area >> - pmd_trans_huge, pmd_devmap, and migration entry validation are >> performed >> >> To leverage page_vma_mapped_walk's work, moving TTU_SPLIT_HUGE_PMD >> handling to the while loop checking and removing these duplicate checks >> from split_huge_pmd_locked. >> >> Suggested-by: David Hildenbrand >> Link: https://lore.kernel.org/all/98d1d195-7821-4627-b518-83103ade56c0@redhat.com/ >> Link: https://lore.kernel.org/all/91599a3c-e69e-4d79-bac5-5013c96203d7@redhat.com/ >> Signed-off-by: Gavin Guo >> Acked-by: David Hildenbrand >> --- > > I wonder if we need a WARN here to make sure when THP migration support is not > present all PMDs are split in try_to_migrate_one(). Can you elaborate on the condition you have in mind? If we have TTU_SPLIT_HUGE_PMD set, we'll never reach that point. Without CONFIG_ARCH_ENABLE_THP_MIGRATION, we should be running into the VM_BUG_ON_FOLIO(!pvmw.pte, folio); right? -- Cheers, David / dhildenb