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[2003:cb:c74e:ff00:f734:227:6936:cdab]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a073e5e345sm277581f8f.94.2025.04.24.13.44.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Apr 2025 13:44:13 -0700 (PDT) Message-ID: <91599a3c-e69e-4d79-bac5-5013c96203d7@redhat.com> Date: Thu, 24 Apr 2025 22:44:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: Simplify the split_huge_pmd_locked function To: Gavin Guo , linux-mm@kvack.org, akpm@linux-foundation.org Cc: gshan@redhat.com, willy@infradead.org, ziy@nvidia.com, linmiaohe@huawei.com, hughd@google.com, revest@google.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org References: <20250424105012.427390-1-gavinguo@igalia.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250424105012.427390-1-gavinguo@igalia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: cHdGRt6GrvASdertEZN6WSnQ4tmxxIZufPpHvuVqqSs_1745527454 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 171F9100002 X-Stat-Signature: 6s7rfd9wjgatan7fiipxog14dtj8z4se X-HE-Tag: 1745527457-558835 X-HE-Meta: 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 E8lE7Q6h 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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 24.04.25 12:50, 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, removing these duplicate checks > from split_huge_pmd_locked and also removing the unnecessary folio > argument since it's no longer needed for the validation. > > Suggested-by: David Hildenbrand > Link: https://lore.kernel.org/all/98d1d195-7821-4627-b518-83103ade56c0@redhat.com/ > Signed-off-by: Gavin Guo > --- One could maybe split up the patch into a a) Adjust try_to_migrate_one() + split_huge_pmd_locked() internals b) Remove all the useless folio pointers we pass then around [...] > > void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, > - pmd_t *pmd, bool freeze, struct folio *folio) > + pmd_t *pmd, bool freeze) > { > - bool pmd_migration = is_pmd_migration_entry(*pmd); > - > - VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio)); > VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); > - VM_WARN_ON_ONCE(folio && !folio_test_locked(folio)); > - VM_BUG_ON(freeze && !folio); > - > - /* > - * When the caller requests to set up a migration entry, we > - * require a folio to check the PMD against. Otherwise, there > - * is a risk of replacing the wrong folio. > - */ > - if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || pmd_migration) { > - /* > - * Do not apply pmd_folio() to a migration entry; and folio lock > - * guarantees that it must be of the wrong folio anyway. > - */ > - if (folio && (pmd_migration || folio != pmd_folio(*pmd))) > - return; > + if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || > + is_pmd_migration_entry(*pmd)) { > __split_huge_pmd_locked(vma, pmd, address, freeze); Can drop the {} > } > } > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, [...] > @@ -2291,13 +2291,6 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > if (flags & TTU_SYNC) > pvmw.flags = PVMW_SYNC; > > - /* > - * unmap_page() in mm/huge_memory.c is the only user of migration with > - * TTU_SPLIT_HUGE_PMD and it wants to freeze. > - */ > - if (flags & TTU_SPLIT_HUGE_PMD) > - split_huge_pmd_address(vma, address, true, folio); > - > /* > * For THP, we have to assume the worse case ie pmd for invalidation. > * For hugetlb, it could be much worse if we need to do pud > @@ -2323,9 +2316,21 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > mmu_notifier_invalidate_range_start(&range); > > while (page_vma_mapped_walk(&pvmw)) { > -#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > /* PMD-mapped THP migration entry */ > if (!pvmw.pte) { > + /* > + * unmap_folio() in mm/huge_memory.c is the only user of > + * migration with TTU_SPLIT_HUGE_PMD and it wants to > + * freeze. > + */ I think we drop that comment. Freezing is really the only reasonable thing to do here, because freezing is unmapping a PMD-mapped THP and installing a PTE table with PTE migration entries. (the term freezing is misleading ...) There is one case where "freezing" might fail (if the THP is exclusive and pinned), and that should be handled as expected I think: the caller must check folio_mapped() either way to make sure everything is really unmapped. Thanks! Acked-by: David Hildenbrand -- Cheers, David / dhildenb