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[2003:d8:2f30:5a00:b30d:e6bc:74c3:d6f2]) by smtp.gmail.com with ESMTPSA id k16-20020a05600c0b5000b003fba6709c68sm18788978wmr.47.2023.07.03.13.46.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Jul 2023 13:46:15 -0700 (PDT) Message-ID: <86e1bd0d-c36f-669f-c559-8f99d084ad38@redhat.com> Date: Mon, 3 Jul 2023 22:46:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: Folio mapcount To: Zi Yan , "Yin, Fengwei" Cc: Matthew Wilcox , linux-mm@kvack.org, Vishal Moola , Hugh Dickins , Rik van Riel References: <7DCA075B-1E43-47B1-9402-66C54513D52E@nvidia.com> <310c4d8a-e14c-742b-5c6c-018c01ed897e@intel.com> <957ea888-a96b-89cc-29e2-973bb9e36f40@intel.com> <6cec6f68-248e-63b4-5615-9e0f3f819a0a@redhat.com> <2AE20377-9111-4BCF-879E-7414808BDBA4@nvidia.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <2AE20377-9111-4BCF-879E-7414808BDBA4@nvidia.com> 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: B4A5FA0009 X-Rspam-User: X-Stat-Signature: uprwz6x85kqdkxg8u3b9tpsp3px784zr X-Rspamd-Server: rspam03 X-HE-Tag: 1688417178-47683 X-HE-Meta: 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 /+zAgKAW c+zOFDPlq49eeZUdYWUL360cqvcxWywhUNMLAn9X4K1HO3Sg9ibqW4M3QSOTK1Fb6v42nafFnvKhE5oS7CSfvrvgA9aYxJZXcdxtXp5S/YHXs8+T1jIBN/yb45mUbqAQCEOL4iZh3iKNlqQVfut61OaXVKL1wCs3Q6errfxJf5VX0+7DIvVUzEB5ECD2mcY50Fv/E/sFVTvZtcD/7sPldHINiT0Ev9AvryVTdtxwLdT8FAojU6VRQcjOqguym7Jl/1tHBdldrNSApHWojLnRC5Lh9IkN9ansl59DWLFGWAqO8gQWU5jLP6yUpYzUw21XJyTTsTo+Z4/IPZNFi4mxfSz+3Bl70E0DqhrI4q9ZCCD1ZClNP/IOFxsBUp4EgDWJK80gHqdE+tnNz9mqmOzfqGYqEWyzh5L/YneWHgFsrqB0k1XYmGv5485NRnR3GpcsIJzDk 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: On 03.07.23 15:24, Zi Yan wrote: > On 2 Jul 2023, at 21:09, Yin, Fengwei wrote: > >> On 7/3/2023 3:51 AM, Zi Yan wrote: >>>> (3) Mapcount of first (or any other) subpage (compount+subpage): for >>>> folio_estimated_sharers(). >>> This is another estimation. I wonder if we can use a different estimation >>> like total_mapcount() > folio_nr_pages() instead. >> Considering the partial folio mapping, I suppose we should use >> total_mapcount() > folio->_nr_pages_mapped >> as folio_estimated_sharers(). > > What you propose is to get a precise check instead of estimate, and you assume no PMD mapping and still require per-page mapcount. > > What I am proposing is to get rid of per-page mapcount, which is my goal, and use a single mapcount to do a rough estimate. ... and I am (a) not sure it's desirable to only have a single mapcount just for the sake of it (b) for something that's PMD mappable (IOW, 2 MiB THP), the overhead of having 1 vs. 2 vs. 3. mapcount is pretty insignificant. 512 vs. 3 is still a big win. ... but again, I have to finish my homework first to make sure I haven't missed any corner cases. -- Cheers, David / dhildenb