linux-kernel - Re: [PATCH v2 0/5] ksm: support tracking KSM-placed zero-pages

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Message-Id: <20221011023109.322501-1-xu.xin16@zte.com.cn>
Date:   Tue, 11 Oct 2022 02:31:09 +0000
From:   xu xin <xu.xin.sc@...il.com>
To:     imbrenda@...ux.ibm.com
Cc:     akpm@...ux-foundation.org, david@...hat.com,
        jiang.xuexin@....com.cn, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, ran.xiaokai@....com.cn, xu.xin.sc@...il.com,
        xu.xin16@....com.cn, yang.yang29@....com.cn
Subject: Re: [PATCH v2 0/5] ksm: support tracking KSM-placed zero-pages

>
>> Hello, Thanks for your reply.
>> 
>> >
>> >why are you trying so hard to fix something that is not broken?  
>> 
>> Actually, it breaks the definition of unmerge, though it's usually not a big
>> problem.
>> >
>> >can't you just avoid using use_zero_pages?  
>> 
>> use_zero_pages is good, not just because of cache colouring as described in doc,
>> but also because use_zero_pages can accelerate merging empty pages when there
>> are plenty of empty pages (full of zeros) as the time of page-by-page comparision
>> (unstable_tree_search_insert) is saved.
>
>interesting, this is some useful information that you could have written
>in the cover letter and/or commit messages, to explain why you are
>proposing these changes :)

Yes. I have done it in v3. 
Thanks.  
>
>> 
>> >
>> >why is it so important to know how many zero pages have been merged?
>> >and why do you want to unmerge them?  
>> 
>> Zero pages may be the most common merged pages in actual environment(not only VM but
>
>also interesting information, which you could also have written in the
>cover letter and/or commit messages
>
>> also including other application like containers). Sometimes customers (app developers)
>> are very interested in how many non-zero-pages are actually merged in their apps.
>> 
>> >
>> >the important thing is that the sysadmin knows how much memory would be
>> >needed to do the unmerge, and that information is already there.
>> >  
>> 
>> I think it's about chicken-and-egg problem.
>> 
>> 
>> Anyway, thanks for your reply.
>>