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[149.14.88.26]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ae353c6bea1sm1229554266b.146.2025.07.03.02.25.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 03 Jul 2025 02:25:53 -0700 (PDT) Message-ID: <1d82c930-be52-4983-9fd7-099df487eb48@redhat.com> Date: Thu, 3 Jul 2025 11:25:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] khugepaged: Reduce race probability between migration and khugepaged To: Dev Jain , akpm@linux-foundation.org Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250703054823.49149-1-dev.jain@arm.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: <20250703054823.49149-1-dev.jain@arm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: figcWDLwuWEoahe_imoxJFYBQT0CsGvaJrGQAGDHSQI_1751534755 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: rspam06 X-Rspamd-Queue-Id: B5B7A12000D X-Stat-Signature: 47gfbytyw1xfxxkegaxpzu4ozhgt9e5i X-HE-Tag: 1751534758-850944 X-HE-Meta: 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 Ihfv501D 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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 03.07.25 07:48, Dev Jain wrote: > Suppose a folio is under migration, and khugepaged is also trying to > collapse it. collapse_pte_mapped_thp() will retrieve the folio from the > page cache via filemap_lock_folio(), thus taking a reference on the folio > and sleeping on the folio lock, since the lock is held by the migration > path. Migration will then fail in > __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of > such a race happening (leading to migration failure) by bailing out > if we detect a PMD is marked with a migration entry. > > This fixes the migration-shared-anon-thp testcase failure on Apple M3. > > Note that, this is not a "fix" since it only reduces the chance of > interference of khugepaged with migration, wherein both the kernel > functionalities are deemed "best-effort". > > Signed-off-by: Dev Jain > --- > > v1->v2: > - Remove SCAN_PMD_MIGRATION, merge into SCAN_PMD_MAPPED (David, Anshuman) > - Add a comment (Lorenzo) > > v1: > - https://lore.kernel.org/all/20250630044837.4675-1-dev.jain@arm.com/ > > mm/khugepaged.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 1aa7ca67c756..3fdefc4f4984 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -941,6 +941,15 @@ static inline int check_pmd_state(pmd_t *pmd) > > if (pmd_none(pmde)) > return SCAN_PMD_NONE; > + > + /* > + * The folio may be under migration when khugepaged is trying to > + * collapse it. Migration success or failure will eventually end > + * up with the PMD still pointing to a PMD-order folio, so return > + * SCAN_PMD_MAPPED. Nit: the last part (, so return ..) is obvious from the code. I would have written /* * The folio may be under migration when khugepaged is trying to * collapse it. Migration success or failure will eventually end * up with a present PMD entry again. */ Acked-by: David Hildenbrand -- Cheers, David / dhildenb