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[2003:d8:2f1a:7c00:4ac1:c2c4:4167:8a0f]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d1fe0636dsm62023085e9.11.2025.03.15.16.02.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 15 Mar 2025 16:03:00 -0700 (PDT) Message-ID: <78e2ceb6-e4ab-4acb-b680-bb3384fe3856@redhat.com> Date: Sun, 16 Mar 2025 00:02:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/5] mm: Separate folio_split_memcg_refs() from split_page_memcg() To: Zi Yan Cc: "Matthew Wilcox (Oracle)" , Andrew Morton , linux-mm@kvack.org, Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song References: <20250314133617.138071-1-willy@infradead.org> <20250314133617.138071-2-willy@infradead.org> <6F69A825-CF2B-4065-850C-C0283C3C8F41@nvidia.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: <6F69A825-CF2B-4065-850C-C0283C3C8F41@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: y3sSAAWsTrtJNXYI_Su2p_W1_3kuVY9HZ43bipwo7ZM_1742079781 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: gujaq5pc5hbpbak3i71b7oy7aphe9azm X-Rspamd-Queue-Id: E36E5C0004 X-HE-Tag: 1742079784-135934 X-HE-Meta: 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 df8ilpLk 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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 15.03.25 00:15, Zi Yan wrote: > On 14 Mar 2025, at 17:49, David Hildenbrand wrote: > >> On 14.03.25 14:36, Matthew Wilcox (Oracle) wrote: >>> Folios always use memcg_data to refer to the mem_cgroup while pages >>> allocated with GFP_ACCOUNT have a pointer to the obj_cgroup. Since the >>> caller already knows what it has, split the function into two and then >>> we don't need to check. >>> >>> Move the assignment of split folio memcg_data to the point where we set >>> up the other parts of the new folio. That leaves folio_split_memcg_refs() >>> just handling the memcg accounting. >>> >>> Signed-off-by: Matthew Wilcox (Oracle) >>> Acked-by: Johannes Weiner >>> Acked-by: Shakeel Butt >>> Acked-by: Zi Yan >>> --- >>> include/linux/memcontrol.h | 7 +++++++ >>> mm/huge_memory.c | 16 ++++------------ >>> mm/memcontrol.c | 17 +++++++++++++---- >>> 3 files changed, 24 insertions(+), 16 deletions(-) >>> >>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >>> index 57664e2a8fb7..d090089c5497 100644 >>> --- a/include/linux/memcontrol.h >>> +++ b/include/linux/memcontrol.h >>> @@ -1039,6 +1039,8 @@ static inline void memcg_memory_event_mm(struct mm_struct *mm, >>> } >>> void split_page_memcg(struct page *head, int old_order, int new_order); >>> +void folio_split_memcg_refs(struct folio *folio, unsigned old_order, >>> + unsigned new_order); >>> static inline u64 cgroup_id_from_mm(struct mm_struct *mm) >>> { >>> @@ -1463,6 +1465,11 @@ static inline void split_page_memcg(struct page *head, int old_order, int new_or >>> { >>> } >>> +static inline void folio_split_memcg_refs(struct folio *folio, >>> + unsigned old_order, unsigned new_order) >>> +{ >>> +} >>> + >>> static inline u64 cgroup_id_from_mm(struct mm_struct *mm) >>> { >>> return 0; >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 14b1963898a7..3e5ecc8f3d13 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3394,6 +3394,9 @@ static void __split_folio_to_order(struct folio *folio, int old_order, >>> folio_set_young(new_folio); >>> if (folio_test_idle(folio)) >>> folio_set_idle(new_folio); >>> +#ifdef CONFIG_MEMCG >>> + new_folio->memcg_data = folio->memcg_data; >>> +#endif >>> folio_xchg_last_cpupid(new_folio, folio_last_cpupid(folio)); >>> } >>> @@ -3525,18 +3528,7 @@ static int __split_unmapped_folio(struct folio *folio, int new_order, >>> } >>> } >>> - /* >>> - * Reset any memcg data overlay in the tail pages. >>> - * folio_nr_pages() is unreliable until prep_compound_page() >>> - * was called again. >>> - */ >>> -#ifdef NR_PAGES_IN_LARGE_FOLIO >>> - folio->_nr_pages = 0; >>> -#endif >> >> >> I remember that we could trigger a warning without that, but I don't immediately find where that warning was. IIRC, if we'd split to order-0, page[1] would have indicated that it had a memcg set, and something bailed out. >> >> Maybe Zi Yan recalls where that check fired. > > The error I encountered is different. When I rebase my folio_split() > on top of David’s mapcount patchset, my original patch used folio_nr_pages() > after memcg split. Since memcg overlays with _nr_pages, when splitting > to order-0, folio->_nr_page is overwritten with memcg_data, causing > folio_nr_pages() to return a bogus value. With Matthew’s this patch, > memcg_data of page[1] is written inside __split_folio_to_order(), > so in theory __split_folio_to_order() can call folio_nr_pages() like > my original patch. Ah, my memory comes back. Right, I fixed that by passing "old_order" instead when rebasing on your series and ... > > For folio->_nr_pages = 0, I suppose it is trying to suppress any > page[1]->memcg_data != NULL check in the following code. But I could > not find any. ... that was likely an issue I ran into before rebasing on your code, where I had to effectively clear page[1]->memcg_data. So all good, clearing folio->_nr_pages can be dropped. -- Cheers, David / dhildenb