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[2003:cb:c720:d600:1d90:f4:74d9:2c94]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39efa43ca78sm7982886f8f.47.2025.04.20.00.12.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 20 Apr 2025 00:12:11 -0700 (PDT) Message-ID: <2e501e48-8604-4813-b76a-d467cad67f53@redhat.com> Date: Sun, 20 Apr 2025 09:12:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/rmap: optimize MM-ID mapcount handling with union To: Lance Yang , akpm@linux-foundation.org Cc: mingzhe.yang@ly.com, willy@infradead.org, ziy@nvidia.com, mhocko@suse.com, vbabka@suse.cz, surenb@google.com, linux-mm@kvack.org, jackmanb@google.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, Lance Yang References: <20250420055159.55851-1-lance.yang@linux.dev> 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: <20250420055159.55851-1-lance.yang@linux.dev> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: xaIyxfVTZwAdRBmxlUaBDv6DaEyH7Qu4MO2cu39ysxM_1745133132 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: ECED7A0008 X-Stat-Signature: ayyb11zoycmue1zsn1i9st1wsu83x4qy X-HE-Tag: 1745133135-979303 X-HE-Meta: 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 P0Myao21 sPzKXArhObLbqLA3hUKqIRXShTI7VctmPWwVpYtuOIW35SqW8Ei576lIM1nlYymUJphqmGqeYqVyAVW3la6dFCBEESuGIWTajZeu3X4QNDgmmD9Mlb0S+cXXQbub93H0i1ZnqMhWiqclROSoUDmLcdXe8Mi5z73KFweSljTEuNrrDb6eY+hACoBuTbLMpEIgGZZBqbR60jjl6mxfQ2g8wF7Kc+leRrS7K+50en+1DdvtolYBKdUZLwCEGuplKF8XZvhwExg8IsJtYs/m8F0J0duep3WxEd+yU9X0Bcip86Dkiy2n7TO7pFkG3TL3gmHMFOUxUNUFd8i88yr/QBTga+QxGDnnRqfxDIoF7FaizZrl4gN9M5PrJAlRjorzWgTMDDiqxA2CX62ddM+smhYaMJtNZcw== 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: > /* Note: mapcounts start at -1. */ > atomic_set(&folio->_large_mapcount, mapcount - 1); > diff --git a/mm/internal.h b/mm/internal.h > index 838f840ded83..1505174178f4 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -772,8 +772,13 @@ static inline void prep_compound_head(struct page *page, unsigned int order) > atomic_set(&folio->_nr_pages_mapped, 0); > if (IS_ENABLED(CONFIG_MM_ID)) { > folio->_mm_ids = 0; > - folio->_mm_id_mapcount[0] = -1; > - folio->_mm_id_mapcount[1] = -1; > + /* > + * One-shot initialization of both mapcount slots to -1. > + * Using 'unsigned long' ensures cross-arch compatibility: > + * - 32-bit: Fills both short slots (0xFFFF each) > + * - 64-bit: Fills both int slots (0xFFFFFFFF each) > + */ > + folio->_mm_id_mapcounts = -1UL; Are we sure the compiler cannot optimize that itself? On x86-64 I get with gcc 14.2.1: ; folio->_mm_id_mapcount[0] = -1; 3f2f: 48 c7 42 60 ff ff ff ff movq $-0x1, 0x60(%rdx) Which should be a quadword (64bit) setting, so exactly what you want to achieve. -- Cheers, David / dhildenb