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[2003:cb:c74f:b800:58e5:8355:5366:573d]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43aba5711fcsm58296895e9.28.2025.02.27.05.50.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Feb 2025 05:50:13 -0800 (PST) Message-ID: <5bb20271-a92a-454e-90e7-8812fd01d31d@redhat.com> Date: Thu, 27 Feb 2025 14:50:12 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] mm: page_owner: use new iteration API To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.org, yuzhao@google.com, pasha.tatashin@soleen.com Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, muchun.song@linux.dev References: <68e82e87-606e-4443-99d3-7de6f665ce05@redhat.com> From: David Hildenbrand Content-Language: en-US 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: <68e82e87-606e-4443-99d3-7de6f665ce05@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 25.02.25 23:30, Luiz Capitulino wrote: > On 2025-02-25 11:44, David Hildenbrand wrote: >> On 24.02.25 22:59, Luiz Capitulino wrote: >>> The page_ext_next() function assumes that page extension objects for a >>> page order allocation always reside in the same memory section, which >>> may not be true and could lead to crashes. Use the new page_ext >>> iteration API instead. >>> >>> Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios") >>> Signed-off-by: Luiz Capitulino >>> --- >>>   mm/page_owner.c | 61 +++++++++++++++++++++++-------------------------- >>>   1 file changed, 29 insertions(+), 32 deletions(-) >>> >> >> [...] >> >>>   void __reset_page_owner(struct page *page, unsigned short order) >>> @@ -293,11 +297,11 @@ void __reset_page_owner(struct page *page, unsigned short order) >>>       page_owner = get_page_owner(page_ext); >>>       alloc_handle = page_owner->handle; >>> +    page_ext_put(page_ext); >>>       handle = save_stack(GFP_NOWAIT | __GFP_NOWARN); >>> -    __update_page_owner_free_handle(page_ext, handle, order, current->pid, >>> +    __update_page_owner_free_handle(page, handle, order, current->pid, >>>                       current->tgid, free_ts_nsec); >>> -    page_ext_put(page_ext); >> >> I assume moving that is fine ... >> >> but I'll not that ... >> >>> -    for (i = 0; i < (1 << new_page_owner->order); i++) { >>> +    rcu_read_lock(); >>> +    for_each_page_ext(&old->page, 1 << new_page_owner->order, page_ext, iter) { >>> +        old_page_owner = get_page_owner(page_ext); >>>           old_page_owner->handle = migrate_handle; >>> -        old_ext = page_ext_next(old_ext); >>> -        old_page_owner = get_page_owner(old_ext); >>>       } >>> +    rcu_read_unlock(); >>>       page_ext_put(new_ext); >>>       page_ext_put(old_ext); >> >> ... here you are not moving it? >> >> >> In general, LGTM, only the remaining page_ext_put() are a bit confusing. > > Which part you found confusing: the fact that I'm not moving them up or that > we still make use of them? How we are deferring page_ext_put() when not actually working on these values anymore. The page_owner itself should not go away here unless we have a serious bug. To be precise, can't we simply do the following on top? diff --git a/mm/page_owner.c b/mm/page_owner.c index c9d2c688eb981..12044340adf89 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -356,26 +356,24 @@ void __split_page_owner(struct page *page, int old_order, int new_order) void __folio_copy_owner(struct folio *newfolio, struct folio *old) { - struct page_ext *old_ext; - struct page_ext *new_ext; struct page_ext *page_ext; struct page_ext_iter iter; struct page_owner *old_page_owner; struct page_owner *new_page_owner; depot_stack_handle_t migrate_handle; - old_ext = page_ext_get(&old->page); - if (unlikely(!old_ext)) + page_ext = page_ext_get(&old->page); + if (unlikely(!page_ext)) return; + old_page_owner = get_page_owner(page_ext); + page_ext_put(page_ext); - new_ext = page_ext_get(&newfolio->page); - if (unlikely(!new_ext)) { - page_ext_put(old_ext); + page_ext = page_ext_get(&newfolio->page); + if (unlikely(!page_ext)) return; - } + new_page_owner = get_page_owner(page_ext); + page_ext_put(page_ext); - old_page_owner = get_page_owner(old_ext); - new_page_owner = get_page_owner(new_ext); migrate_handle = new_page_owner->handle; __update_page_owner_handle(&newfolio->page, old_page_owner->handle, old_page_owner->order, old_page_owner->gfp_mask, @@ -402,9 +400,6 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old) old_page_owner->handle = migrate_handle; } rcu_read_unlock(); - - page_ext_put(new_ext); - page_ext_put(old_ext); } void pagetypeinfo_showmixedcount_print(struct seq_file *m, -- Cheers, David / dhildenb