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[2003:cb:c702:bf00:abf6:cc3a:24d6:fa55]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42286fe7629sm14175805e9.10.2024.06.12.00.22.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Jun 2024 00:22:27 -0700 (PDT) Message-ID: <2d0df7ca-2720-4a0c-95c5-9b665a567e5f@redhat.com> Date: Wed, 12 Jun 2024 09:22:25 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] mm/highmem: make nr_free_highpages() return "unsigned long" To: Wei Yang Cc: Oscar Salvador , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton References: <20240607083711.62833-1-david@redhat.com> <20240607083711.62833-3-david@redhat.com> <99073d55-5b18-4ed2-b860-8c09e056f585@redhat.com> <20240611005636.g6525rkqpos43yds@master> <04b3dda2-c6a8-4f26-90b8-75fe7580d63e@redhat.com> <20240612070144.q6rpbq2hkwtielav@master> 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: <20240612070144.q6rpbq2hkwtielav@master> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DBC341C000C X-Rspamd-Server: rspam10 X-Rspam-User: X-Stat-Signature: agdobm3xaa8x5ehf6pwp1oyfoyuuipcp X-HE-Tag: 1718176953-871092 X-HE-Meta: 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 3clumqF/ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, 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 12.06.24 09:01, Wei Yang wrote: > On Tue, Jun 11, 2024 at 11:20:00AM +0200, David Hildenbrand wrote: >> On 11.06.24 02:56, Wei Yang wrote: >>> On Mon, Jun 10, 2024 at 10:22:49AM +0200, David Hildenbrand wrote: >>>> On 10.06.24 05:40, Oscar Salvador wrote: >>>>> On Fri, Jun 07, 2024 at 10:37:11AM +0200, David Hildenbrand wrote: >>>>>> It looks rather weird that totalhigh_pages() returns an >>>>>> "unsigned long" but nr_free_highpages() returns an "unsigned int". >>>>>> >>>>>> Let's return an "unsigned long" from nr_free_highpages() to be >>>>>> consistent. >>>>>> >>>>>> While at it, use a plain "0" instead of a "0UL" in the !CONFIG_HIGHMEM >>>>>> totalhigh_pages() implementation, to make these look alike as well. >>>>>> >>>>>> Signed-off-by: David Hildenbrand >>>>> ... >>>>>> -static inline unsigned int nr_free_highpages(void) { return 0; } >>>>>> -static inline unsigned long totalhigh_pages(void) { return 0UL; } >>>>>> +static inline unsigned long nr_free_highpages(void) { return 0; } >>>>>> +static inline unsigned long totalhigh_pages(void) { return 0; } >>>>> >>>>> Although I doubt it has any consequences, I would just leave them both with UL, >>>>> so the return type is consistent with what we are returning. >>>> >>>> These suffixes are only required when using constants that would not fit >>>> into the native (int) type, or converting from that native (int) type to >>>> something else automatically by the compiler would mess things up (for example, >>>> undesired sign extension). For 0 that is certainly impossible :) >>>> >>>> >>>> That's also the reason why in include/linux we now have: >>>> >>>> t14s: ~/git/linux/include/linux $ git grep "return 0UL;" >>>> skbuff.h: return 0UL; >>>> uaccess.h:static inline unsigned long user_access_save(void) { return 0UL; } >>>> t14s: ~/git/linux/include/linux $ git grep "0UL;" >>>> bitmap.h: *dst = ~0UL; >>>> dax.h: return ~0UL; >>>> mtd/map.h: r.x[i] = ~0UL; >>>> netfilter.h: return ((ul1[0] ^ ul2[0]) | (ul1[1] ^ ul2[1])) == 0UL; >>>> skbuff.h: return 0UL; >>>> uaccess.h:static inline unsigned long user_access_save(void) { return 0UL; } >>>> >>>> >>>> ... compared to a long list if "unsigned long" functions that simply "return 0;" >>>> >>> >>> Seems this is the current status. >>> >>> Then my question is do we have a guide line for this? Or 0 is the special >>> case? Sounds positive value has no sign extension problem. If we need to >>> return 1, we suppose to use 1 or 1UL? I found myself confused. >>> >>> I grepped "return 1" and do find some cases without UL: >>> >>> backing-dev.h: wb_stat_error() return 1 for unsigned long. >>> pgtable.h: pte_batch_hint() return 1 for unsigned int. >>> >>> So the guide line is for positive value, it is not necessary to use UL? >> >> I think when returning simple values (0/1/-1), we really don't need these >> suffices at all. The standard says "The type of an integer constant is the >> first of the corresponding list in which its value can be represented.". I >> thought it would always use an "int", but that is not the case. >> >> So, if we use "-1", the compiler will use an "int", and sign extension to >> "unsigned" long will do the right thing. >> >> Simple test: >> >> -1 results in: 0xffffffffffffffff >> -1U results in: 0xffffffff >> -1UL results in: 0xffffffffffffffff >> 0xffffffff results in: 0xffffffff >> 0xffffffffU results in: 0xffffffff >> 0xffffffffUL results in: 0xffffffff >> ~0xffffffff results in: 0x0 >> ~0xffffffffU results in: 0x0 >> ~0xffffffffUL results in: 0xffffffff00000000 >> 0xffffffffffffffff results in: 0xffffffffffffffff >> 0xffffffffffffffffU results in: 0xffffffffffffffff > > I expect this to be 0xffffffff. Why this extend it to a UL? Apparently, the "U" only restricts the set of types to "unsigned ones". https://en.cppreference.com/w/cpp/language/integer_literal So the compiler will use the first "unsigned" type that can hold that value. -- Cheers, David / dhildenb