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[91.12.106.22]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39c301b8ad6sm11414372f8f.56.2025.04.07.00.07.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Apr 2025 00:07:34 -0700 (PDT) Message-ID: Date: Mon, 7 Apr 2025 09:07:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/memory_hotplug: fix call folio_test_large with tail page in do_migrate_range To: Andrew Morton Cc: Jinjiang Tu , osalvador@suse.de, nao.horiguchi@gmail.com, zi.yan@cs.rutgers.edu, linux-mm@kvack.org, wangkefeng.wang@huawei.com, sunnanyong@huawei.com References: <20250324131750.1551884-1-tujinjiang@huawei.com> <899807c3-931f-43e6-bf3e-188787a4205a@redhat.com> <68ab727b-dc3d-327f-33b6-25bbfce8530e@huawei.com> <20250328163700.82c9b426bf199102f3d90dcd@linux-foundation.org> <0a636dd6-3d19-4a3b-8645-21c7b85a4aff@redhat.com> <20250406185924.451276bf79b7a26fe5ae7ae4@linux-foundation.org> 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: <20250406185924.451276bf79b7a26fe5ae7ae4@linux-foundation.org> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: dVFOD1YxKey7q2KuhmroxhS56ct2h5QTbNR0IRksZT8_1744009656 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: BA342140007 X-Stat-Signature: w6neuso36h64apog333n5otroiaii1xr X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1744009660-262365 X-HE-Meta: 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 SkD5psq4 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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 07.04.25 03:59, Andrew Morton wrote: > On Tue, 1 Apr 2025 18:44:06 +0200 David Hildenbrand wrote: > >> On 29.03.25 00:37, Andrew Morton wrote: >>> On Tue, 25 Mar 2025 20:05:50 +0100 David Hildenbrand wrote: >>> >>>> On 25.03.25 04:02, Jinjiang Tu wrote: >>>>> >>>>>> Moving that will not make it able to skip the large frozen >>>>>> (refcount==0, e.g., free hugetlb) folio in the continue/put_folio case >>>>>> above. Hmmmm .. >>>>> For free hugetlb, pfn is increased by 1 in each loop. This leads to skip >>>>> free hugetlb slower. >>>> >>>> Yes. But now I realize that we have the same issue with free buddy pages >>>> already (folio_try_get of each individual page :( ). >>>> >>>>>> >>>>>> We could similarly to dumping folios, snapshot them, so we can read >>>>>> stable data. >>>>> extract the code in __dump_page()? But snapshot may lead to >>>>> do_migrate_range() slower too. >>>> >>>> There is a patch series on the list to do that, but it might take a >>>> while to clean that up. Ideally, we'd also jump over free buddy pages. >>>> In the future we might have better ways to do that. >>>> >>>> I don't consider this change here really important, but if all it >>>> affects is free hugetlb folios, it's not really worth it to have this >>>> code around. >>>> >>>> Acked-by: David Hildenbrand >>>> >>>> But: I suspect 8135d8926c08 is not the introducing commit. Please re-verify. >>>> >>>> We should not CC stable. >>> >> >> Sorry for the late reply. >> >>> Why shouldn't we cc:stable? A userspace-triggerable BUG? >> >> My reasoning was that it's a VM_BUG_ON_PAGE, and nothing is actually >> broken on !CONFIG_DEBUG_VM systems ... combined with hugetlb allocation >> and memory offlining usually being rare and usually privileged operations. >> >> It would be a different story if the VM_BUG_ON_PAGE revealed an actual >> issue; but this is a well documented race. >> >> One might argue that unplugging a DIMM could automatically trigger it >> (rare operation ..), and as we discovered in the meantime, THPs are also >> affected. But again, CONFIG_VM_DEBUG ... which even Fedora stopped setting. >> >> So I don't think CC stable is warranted here, but I wouldn't object if >> there are good reasons to do it: like assuming that there are >> CONFIG_VM_DEBUG stable users out there that rely on these features. > > Oh. I thought that quite a few distros use CONFIG_DEBUG_VM. Fedora used to be the prime example people kept mentioning. But they stopped using it for performance reasons IIRC. -- Cheers, David / dhildenb