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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-390e47a6a9fsm20821992f8f.36.2025.03.05.02.29.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Mar 2025 02:29:55 -0800 (PST) Message-ID: Date: Wed, 5 Mar 2025 11:29:54 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 03/20] mm: let _folio_nr_pages overlay memcg_data in first tail page To: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, Andrew Morton , "Matthew Wilcox (Oracle)" , Tejun Heo , Zefan Li , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , "Kirill A. Shutemov" , Stephen Rothwell References: <20250303163014.1128035-1-david@redhat.com> <20250303163014.1128035-4-david@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: <20250303163014.1128035-4-david@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 03.03.25 17:29, David Hildenbrand wrote: > Let's free up some more of the "unconditionally available on 64BIT" > space in order-1 folios by letting _folio_nr_pages overlay memcg_data in > the first tail page (second folio page). Consequently, we have the > optimization now whenever we have CONFIG_MEMCG, independent of 64BIT. > > We have to make sure that page->memcg on tail pages does not return > "surprises". page_memcg_check() already properly refuses PageTail(). > Let's do that earlier in print_page_owner_memcg() to avoid printing > wrong "Slab cache page" information. No other code should touch that > field on tail pages of compound pages. > > Reset the "_nr_pages" to 0 when splitting folios, or when freeing them > back to the buddy (to avoid false page->memcg_data "bad page" reports). > > Note that in __split_huge_page(), folio_nr_pages() would stop working > already as soon as we start messing with the subpages. > > Most kernel configs should have at least CONFIG_MEMCG enabled, even if > disabled at runtime. 64byte "struct memmap" is what we usually have > on 64BIT. > > While at it, rename "_folio_nr_pages" to "_nr_pages". > > Hopefully memdescs / dynamically allocating "strut folio" in the future > will further clean this up, e.g., making _nr_pages available in all > configs and maybe even in small folios. Doing that should be fairly easy > on top of this change. > > Reviewed-by: Kirill A. Shutemov > Signed-off-by: David Hildenbrand > --- > include/linux/mm.h | 4 ++-- > include/linux/mm_types.h | 30 ++++++++++++++++++++++-------- > mm/huge_memory.c | 16 +++++++++++++--- > mm/internal.h | 4 ++-- > mm/page_alloc.c | 6 +++++- > mm/page_owner.c | 2 +- > 6 files changed, 45 insertions(+), 17 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a743321dc1a5d..694704217df8a 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1199,10 +1199,10 @@ static inline unsigned int folio_large_order(const struct folio *folio) > return folio->_flags_1 & 0xff; > } > > -#ifdef CONFIG_64BIT > +#ifdef NR_PAGES_IN_LARGE_FOLIO > static inline long folio_large_nr_pages(const struct folio *folio) > { > - return folio->_folio_nr_pages; > + return folio->_nr_pages; > } > #else > static inline long folio_large_nr_pages(const struct folio *folio) > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 689b2a7461892..e81be20bbabc6 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -287,6 +287,11 @@ typedef struct { > unsigned long val; > } swp_entry_t; > > +#if defined(CONFIG_MEMCG) || defined(CONFIG_SLAB_OBJ_EXT) > +/* We have some extra room after the refcount in tail pages. */ > +#define NR_PAGES_IN_LARGE_FOLIO > +#endif > + > /** > * struct folio - Represents a contiguous set of bytes. > * @flags: Identical to the page flags. > @@ -312,7 +317,7 @@ typedef struct { > * @_large_mapcount: Do not use directly, call folio_mapcount(). > * @_nr_pages_mapped: Do not use outside of rmap and debug code. > * @_pincount: Do not use directly, call folio_maybe_dma_pinned(). > - * @_folio_nr_pages: Do not use directly, call folio_nr_pages(). > + * @_nr_pages: Do not use directly, call folio_nr_pages(). > * @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h. > * @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h. > * @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h. > @@ -377,13 +382,20 @@ struct folio { > unsigned long _flags_1; > unsigned long _head_1; > /* public: */ > - atomic_t _large_mapcount; > - atomic_t _entire_mapcount; > - atomic_t _nr_pages_mapped; > - atomic_t _pincount; > -#ifdef CONFIG_64BIT > - unsigned int _folio_nr_pages; > -#endif > + union { > + struct { > + atomic_t _large_mapcount; > + atomic_t _entire_mapcount; > + atomic_t _nr_pages_mapped; > + atomic_t _pincount; > + }; > + unsigned long _usable_1[4]; > + }; > + atomic_t _mapcount_1; > + atomic_t _refcount_1; > +#ifdef NR_PAGES_IN_LARGE_FOLIO > + unsigned int _nr_pages; > +#endif /* NR_PAGES_IN_LARGE_FOLIO */ > /* private: the union with struct page is transitional */ @Andrew The following on top to make htmldoc happy. There will be two conflicts to be resolved in two patches because of the added "/* private: " under "_pincount". It's fairly straight forward to resolve (just keep "/* private:" below any changes), but let me know if I should resend a v4 instead for this. From 9d9ff38c2ea14f1b4dab29f099ec0f6be683f3fe Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 5 Mar 2025 11:14:52 +0100 Subject: [PATCH] fixup: mm: let _folio_nr_pages overlay memcg_data in first tail page Make "make htmldoc" happy by marking non-private placeholder entries private. Signed-off-by: David Hildenbrand --- include/linux/mm_types.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index e81be20bbabc..6062c12c3871 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -381,18 +381,20 @@ struct folio { struct { unsigned long _flags_1; unsigned long _head_1; - /* public: */ union { struct { + /* public: */ atomic_t _large_mapcount; atomic_t _entire_mapcount; atomic_t _nr_pages_mapped; atomic_t _pincount; + /* private: the union with struct page is transitional */ }; unsigned long _usable_1[4]; }; atomic_t _mapcount_1; atomic_t _refcount_1; + /* public: */ #ifdef NR_PAGES_IN_LARGE_FOLIO unsigned int _nr_pages; #endif /* NR_PAGES_IN_LARGE_FOLIO */ -- 2.48.1 -- Cheers, David / dhildenb