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Date:   Mon, 10 Oct 2022 15:42:48 +0200
From:   Claudio Imbrenda <imbrenda@linux.ibm.com>
To:     xu xin <xu.xin.sc@gmail.com>
Cc:     akpm@linux-foundation.org, david@redhat.com,
        jiang.xuexin@zte.com.cn, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, ran.xiaokai@zte.com.cn, xu.xin16@zte.com.cn,
        yang.yang29@zte.com.cn
Subject: Re: [PATCH v2 0/5] ksm: support tracking KSM-placed zero-pages
Message-ID: <20221010154248.1ee86294@p-imbrenda>
In-Reply-To: <20221010120834.318840-1-xu.xin16@zte.com.cn>
References: <20221010112413.219dc989@p-imbrenda>
        <20221010120834.318840-1-xu.xin16@zte.com.cn>
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On Mon, 10 Oct 2022 12:08:34 +0000
xu xin <xu.xin.sc@gmail.com> wrote:

> 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 :)

> 
> >
> >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.
>