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[2003:cb:c705:6d00:5870:9639:1c17:8162]) by smtp.gmail.com with ESMTPSA id q3-20020a1ce903000000b003dfdeb57027sm16905905wmc.38.2023.02.13.04.44.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Feb 2023 04:44:08 -0800 (PST) Message-ID: Date: Mon, 13 Feb 2023 13:44:07 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [PATCH v5 2/6] ksm: support unsharing zero pages placed by KSM To: yang.yang29@zte.com.cn 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, xu.xin.sc@gmail.com, xu.xin16@zte.com.cn References: <202302041418359766772@zte.com.cn> From: David Hildenbrand Organization: Red Hat In-Reply-To: <202302041418359766772@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-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2645B100009 X-Stat-Signature: 5yfzrjp6ochq35idi5tejnud7dbg68zu X-HE-Tag: 1676292251-35127 X-HE-Meta: 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 t4eHV1UM jO9zWkN5Evu/whH5ny2no6Hk6JlJt9XG8mCHdy0JNk6gtlZytc1pzf8gDnwTcDY4nnYwtkGyP4NkKQO8CAXheOOpOn+L6D1IxTusik4qGtimrFU5EGkG5Aqn2P5ytRc0CyvSPwudDQg01YaGvN0pRlkkU/iPEE3VKjspRln5Rw3ZWcTTwbFTOugr1PRJRSLMkXTG1kdzLRNmRyEdt4Ls0SyTW9lvGkeuPZjQLKXS0qH6f3UoMILYKR3xGHrm79M6az4TUCI6GeHw4VsBp5jx18+V8WEq80RW6NkOKtdA1Thxf1VFTKsKreev8+gYL3EC2Dbyzirzos5SXLkhFB+Q5wCvzC8NUkUE6SEVZnNnY87bk/JqBvU1905WGbzA273S/YqlgB65/5QBnlV1fYupK3Rzr3J7jBfcoZ5zBYwUL1HdOQ002Co3Vndw2aA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000058, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 04.02.23 07:18, yang.yang29@zte.com.cn wrote: [sorry, was on vacation last week] >> Why use flags if they both conditions are mutually exclusive? > > Just to make the return value of break_ksm_pmd_entry() more expressive and > understandable. because break_ksm_pmd_entry have three types of returned > values (0, 1, 2). It adds confusion. Just simplify it please. > >> MADV_UNMERGEABLE -> unmerge_ksm_pages() will never unshare the shared >> zeropage? I thought the patch description mentions that that is one of >> the goals? > > No, MADV_UNMERGEABLE will trigger KSM to unshare the shared zeropages in the > context of "get_next_rmap_item() -> unshare_zero_pages(), but not directly in the > context of " madvise()-> unmerge_ksm_pages() ". The reason for this is to avoid > increasing long delays of madvise() calling on unsharing zero pages. > Why do we care and make this case special? -- Thanks, David / dhildenb