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[2003:cb:c706:ed00:59ee:f048:4ed9:62a6]) by smtp.gmail.com with ESMTPSA id s21-20020a05600c45d500b0040775501256sm14450380wmo.16.2023.11.15.02.49.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Nov 2023 02:49:25 -0800 (PST) Message-ID: Date: Wed, 15 Nov 2023 11:49:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] ksm: delay the check of splitting compound pages To: xu Cc: akpm@linux-foundation.org, imbrenda@linux.ibm.com, jiang.xuexin@zte.com.cn, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ran.xiaokai@zte.com.cn, wang.yong12@zte.com.cn, xu.xin16@zte.com.cn, yang.yang29@zte.com.cn References: <20231115031129.1970581-1-xu.xin16@zte.com.cn> 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: <20231115031129.1970581-1-xu.xin16@zte.com.cn> 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-Stat-Signature: gaunggtoxaj1nq3dymrsjh98uim1gku6 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EDDFD4000A X-Rspam-User: X-HE-Tag: 1700045369-748779 X-HE-Meta: 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 cH6tO84a 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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 15.11.23 04:11, xu wrote: >>> diff --git a/mm/ksm.c b/mm/ksm.c >>> index 7efcc68ccc6e..c952fe5d9e43 100644 >>> --- a/mm/ksm.c >>> +++ b/mm/ksm.c >>> @@ -2229,24 +2229,10 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite >>> tree_rmap_item = >>> unstable_tree_search_insert(rmap_item, page, &tree_page); >>> if (tree_rmap_item) { >>> - bool split; >>> - >>> kpage = try_to_merge_two_pages(rmap_item, page, >>> tree_rmap_item, tree_page); >>> - /* >>> - * If both pages we tried to merge belong to the same compound >>> - * page, then we actually ended up increasing the reference >>> - * count of the same compound page twice, and split_huge_page >>> - * failed. >>> - * Here we set a flag if that happened, and we use it later to >>> - * try split_huge_page again. Since we call put_page right >>> - * afterwards, the reference count will be correct and >>> - * split_huge_page should succeed. >>> - */ >> >> I'm curious, why can't we detect that ahead of time and keep only a >> single reference? Why do we need the backup code? Anything I am missing? > > I don't know the original reason, better ask Claudio Imbrenda . > Maybe because doing detection that ahead of time will break several funtions' semantic, > such as try_to_merge_two_pages(), try_to_merge_with_ksm_page() and try_to_merge_one_page() > > Adding the backup code don't change the old code and fixing the old problem, it's good. It's absolutely counter-intuitive to check for something that cannot possibly work after the effects. This better has a good reason to make that code more complicated. -- Cheers, David / dhildenb