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(p200300d82f259c00e2c76eb58a511c60.dip0.t-ipconnect.de. [2003:d8:2f25:9c00:e2c7:6eb5:8a51:1c60]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-447f6b29619sm72162355e9.7.2025.05.21.05.11.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 May 2025 05:11:47 -0700 (PDT) Message-ID: Date: Wed, 21 May 2025 14:11:44 +0200 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 v4 1/4] mm/page_isolation: make page isolation a standalone bit. To: Zi Yan Cc: Oscar Salvador , Johannes Weiner , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Baolin Wang , "Kirill A . Shutemov" , Mel Gorman , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Richard Chang , linux-kernel@vger.kernel.org References: <20250509200111.3372279-1-ziy@nvidia.com> <20250509200111.3372279-2-ziy@nvidia.com> <506798aa-0280-4f63-9c0e-d5f2f5d58c3c@redhat.com> <166E73A3-02CE-4023-AE0E-022C9C618C33@nvidia.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.05.25 14:00, Zi Yan wrote: > On 21 May 2025, at 7:57, David Hildenbrand wrote: > >> On 21.05.25 13:16, Zi Yan wrote: >>> On 19 May 2025, at 12:42, David Hildenbrand wrote: >>> >>>>>>> +#ifdef CONFIG_MEMORY_ISOLATION >>>>>>> + if (flags & PB_migrate_isolate_bit) >>>>>>> + return MIGRATE_ISOLATE; >>>>>>> +#endif >>>>>> >>>>>> If you call get_pfnblock_flags_mask() with MIGRATETYPE_MASK, how could you ever get PB_migrate_isolate_bit? >>>>> >>>>> MIGRATETYPE_MASK is ((BIT(PB_migratetype_bits) - 1) | PB_migrate_isolate_bit), >>>>> so it gets PB_migrate_isolate_bit. >>>>> >>>> >>>> Oh ... that's confusing. >>>> >>>>>> >>>>>> >>>>>> I think what we should do is >>>>>> >>>>>> 1) Rename get_pfnblock_flags_mask() to get_pfnblock_flags() >>>>>> >>>>>> 2) Remove the mask parameter >>>>>> >>>>>> 3) Perform the masking in all callers. >>>>> >>>>> get_pfnblock_flags_mask() is also used by get_pageblock_skip() to >>>>> get PB_migrate_skip. I do not think we want to include PB_migrate_skip >>>>> in the mask to confuse readers. >>>> >>>> The masking will be handled in the caller. >>>> >>>> So get_pageblock_skip() would essentially do a >>>> >>>> return get_pfnblock_flags() & PB_migrate_skip_bit; >>>> >>>> etc. >>>> >>>>> >>>>>> >>>>>> >>>>>> >>>>>> Maybe, we should convert set_pfnblock_flags_mask() to >>>>>> >>>>>> void set_clear_pfnblock_flags(struct page *page, unsigned long >>>>>> set_flags, unsigned long clear_flags); >>>>>> >>>>>> And better, splitting it up (or providing helpers) >>>>>> >>>>>> set_pfnblock_flags(struct page *page, unsigned long flags); >>>>>> clear_pfnblock_flags(struct page *page, unsigned long flags); >>>>>> >>>>>> >>>>>> This implies some more code cleanups first that make the code easier to extend. >>>>>> >>>>> >>>>> The same due to PB_migrate_skip. >>>>> >>>>> Based on your suggestion, we could make {set,get}_pfnblock_flags_mask() >>>>> internal APIs by prepending "__". They are only used by the new >>>>> {get, set, clear}_pfnblock_flags() and {get, set, clear}_pageblock_{skip, isolate}(). >>>>> Then use {get, set, clear}_pfnblock_flags() for all migratetype operations. >>>>> >>>>> WDYT? >>>> >>>> In general, lgtm. I just hope we can avoid the "_mask" part and just handle it in these functions directly? >>> >>> After implementing {get, set, clear}_pfnblock_flags(), I find that >>> get_pfnblock_flags() is easy like you wrote above, but set and clear are not, >>> since migratetype and skip/isolate bits are in the same word, meaning >>> I will need to first read them out, change the field, then write them back. >> >> Like existing set_pfnblock_flags_mask() I guess, with the try_cmpxchg() loop. > > Are you saying I duplicate the code in set_pfnblock_flags_mask() to implement > set_pfnblock_flags()? Or just replace set_pfnblock_flags_mask() entirely? The latter as possible. > >> >>> But it will cause inconsistency if there is a parallel writer to the same >>> word. So for set and clear, mask is required. >>> >>> I can try to implement {get, set, clear}_pfnblock_bits(page,pfn, bits) to >>> only handle standalone bits by using the given @bits as the mask and >>> {set,get}_pageblock_migratetype() still use the mask. >> >> We'd still have to do the try_cmpxchg() when dealing with multiple bits, right? >> >> For single bits, we could just use set_bit() etc. > > Mel moved from set_bit() to try_cmpxchg() a word for performance reason. I am > not sure we want to move back. In e58469bafd05 we moved from multiple set_bit etc to a cmpxchange. - for (; start_bitidx <= end_bitidx; start_bitidx++, value <<= 1) - if (flags & value) - __set_bit(bitidx + start_bitidx, bitmap); - else - __clear_bit(bitidx + start_bitidx, bitmap); However, when only setting/clearing a single bit (e.g., isolated), set_bit etc should be much cheaper. For multiple bits, the existing try_cmpxchg should be kept IMHO. -- Cheers, David / dhildenb