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[2003:cb:c707:4f00:a44a:5ad6:765a:635]) by smtp.gmail.com with ESMTPSA id w9-20020a05600c474900b00412e5f32591sm12785546wmo.28.2024.03.12.08.45.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Mar 2024 08:45:37 -0700 (PDT) Message-ID: <0f100f04-5833-4f17-addf-9c0a12e80b9b@redhat.com> Date: Tue, 12 Mar 2024 16:45:36 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Always initialise folio->_deferred_list To: Matthew Wilcox Cc: Andrew Morton , linux-mm@kvack.org References: <20240312035017.516865-1-willy@infradead.org> <78d1e235-b055-48ce-a987-e8719163caf7@redhat.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: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 501EB4001E X-Stat-Signature: 1r4x8e8w63fpqt3mdziyjztfpgwrtd7c X-Rspam-User: X-HE-Tag: 1710258341-9511 X-HE-Meta: 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 x/Nhk1h8 0cgrh24xw0gHBUz/nt+/M3o1BmBVv287hBYAEbUA4g8vVnsXNT2O/lcPqXSfC30JGG4UUkAHMkhuW6wiYMAgg3QiQAWn6ovjV8vte8PLhcNNiPmQTk/eP6xYEDYwcisCu0tfsileHvIF/PrNlEht+OSMEiXG7bnBO2kLD5CtBhEx5BQ9+8l36rKVQqWHu/kKVkc9/+/OJ7YBZGtkf3nkzHuT0aQ== 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 12.03.24 16:38, Matthew Wilcox wrote: > On Tue, Mar 12, 2024 at 03:34:13PM +0100, David Hildenbrand wrote: >> On 12.03.24 15:01, Matthew Wilcox wrote: >>> __free_pages(&folio->page, huge_page_order(h)); >> >> Heh, __free_pages() says: >> >> "This function can free multi-page allocations that are not compound pages". >> I suspect that means "can also free compound pages", but it's confusing. > > Sorry. I wrote that documentation and I was focused on one thing, > but failed to think of the other thing ... it can indeed free compound > pages. I'll add this: > > * If the pages were allocated with __GFP_COMP, prefer using put_page() > * to using this function. Also prefer to call put_page() rather than > * calling __free_page() or __free_pages(page, 0). Sounds good. > >> Especially, I thought we recently learned that free hugetlb folios do have a >> refcount of 0? Confusing. > > Yes, that is confusing. This function wouldn't work if the refcount > were 0 (put_page_testzero() would complain). Ah, here we go: > > In __folio_put(), we know that refcount is 0. > __folio_put_large() -> destroy_large_folio -> free_huge_folio > (refcount still 0 here, indeed it asserts it) > If we add it back to the pool, the refcount stays at 0. > But if we're removing it, we call __remove_hugetlb_folio() > which calls folio_ref_unfreeze(). Ah, that's the case I was missing. The joy of hugetlb :) As a side note: hugetlb.c still talks about "destructor" and "dtor". I assume that dates back to the times where we identified hugetlb folios by a deconstrucor in the compound page. -- Cheers, David / dhildenb