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[2003:cb:c726:6800:7ddf:5fc:2ee5:f08a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39eae979620sm1315106f8f.52.2025.04.11.01.28.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Apr 2025 01:28:44 -0700 (PDT) Message-ID: Date: Fri, 11 Apr 2025 10:28:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] fs/dax: fix folio splitting issue by resetting old folio order + _nr_pages To: Matthew Wilcox , Dan Williams Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev, Alison Schofield , Alexander Viro , Christian Brauner , Jan Kara , Andrew Morton , Alistair Popple , Christoph Hellwig References: <20250410091020.119116-1-david@redhat.com> <67f826cbd874f_72052944e@dwillia2-xfh.jf.intel.com.notmuch> <67f82e0e234ea_720529471@dwillia2-xfh.jf.intel.com.notmuch> 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-MFC-PROC-ID: MPVcGx1R_JbX1YA1kFu_C11bhgYtaBZ4lQlg-VC8cm4_1744360126 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: 99003A0005 X-Stat-Signature: o5i947hnogk88pmxqen14j4afh6ch99t X-HE-Tag: 1744360131-757397 X-HE-Meta: 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 dChny/CH k8x5qCBHj3G8lKTDGHAczShjW0EVkHtZs1qTlmWlEJ2u+FR1tY5CKghu6SjPgUUm/Q+uIM2Z0YRGTr43Yh56urGmjP0I4mn3yzPW/qLmquyewtKA0Jfap8pcugeDZBOvER+bEIs75dEP2KXEqK6eonDfnwfhj4pr8Q+9T1w0ZVS5B+5fkV1saYHbnff9nhQ5MGVolYVMzDqomJAzSrJxHdQ2kgc6IlQxjaG4p6kgRM23ax3BJxvTnD8OCUyqGt8qYRJu7M9pGrdusZEyVOdc/NeCJmzPrsLk8ntOs9YXa7iiOjmS35kb5wVGdz18nG7vuzZWuceOyQA4h9YUVj+s/T06P2n9B8CBdJkLALbF3lcfAmVr8FPCzpf9W3+XidSIFz29SPV+KJ84awTLwvlkm8+mEJeJvPlMvbFKwKyCN0GJ5DY/Ig0kfA4Ou/3cJ7SkcsGMdgcXl2uq/Eno= 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 10.04.25 23:54, Matthew Wilcox wrote: > On Thu, Apr 10, 2025 at 01:46:06PM -0700, Dan Williams wrote: >> Matthew Wilcox wrote: >>> On Thu, Apr 10, 2025 at 01:15:07PM -0700, Dan Williams wrote: >>>> For consistency and clarity what about this incremental change, to make >>>> the __split_folio_to_order() path reuse folio_reset_order(), and use >>>> typical bitfield helpers for manipulating _flags_1? >>> >>> I dislike this intensely. It obfuscates rather than providing clarity. >> >> I'm used to pushing folks to use bitfield.h in driver land, but will not >> push it further here. > > I think it can make sense in places. Just not here. > >> What about this hunk? >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 2a47682d1ab7..301ca9459122 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3404,7 +3404,7 @@ static void __split_folio_to_order(struct folio *folio, int old_order, >> if (new_order) >> folio_set_order(folio, new_order); >> else >> - ClearPageCompound(&folio->page); >> + folio_reset_order(folio); >> } > > I think that's wrong. We're splitting this folio into order-0 folios, > but folio_reset_order() is going to modify folio->_flags_1 which is in > the next page. Right, clearing in this context might only make sense at the very start. diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 2a47682d1ab77..4cd8b394b83a5 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3312,6 +3312,8 @@ static void __split_folio_to_order(struct folio *folio, int old_order, long nr_pages = 1 << old_order; long i; + folio_reset_order(folio); + /* * Skip the first new_nr_pages, since the new folio from them have all * the flags from the original folio. While it looks cleaner, it's in practice not required here, because 1) We handle _nr_pages overlay by setting new_folio->memcg_data new_folio->memcg_data = folio->memcg_data; 2) We handle the order by setting new_folio->flags new_folio->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; That should clear all flags (excluding hwpoison), including the order. It's worth noting that in free_pages_prepare(), we handle both using if (compound) { page[1].flags &= ~PAGE_FLAGS_SECOND; #ifdef NR_PAGES_IN_LARGE_FOLIO folio->_nr_pages = 0; #endif -- Cheers, David / dhildenb