linux-kernel - Re: [PATCH v6 5/6] ksm: add zero_pages

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Date:   Tue, 7 Mar 2023 19:51:19 +0100
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     <yang.yang29@....com.cn>
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>
Subject: Re: [PATCH v6 5/6] ksm: add zero_pages_sharing documentation

On Fri, 10 Feb 2023 09:20:42 +0800 (CST)
<yang.yang29@....com.cn> wrote:

> From: xu xin <xu.xin16@....com.cn>
> 
> When enabling use_zero_pages, pages_sharing cannot represent how
> much memory saved indeed. zero_pages_sharing + pages_sharing does.
> add the description of zero_pages_sharing.
> 
> Cc: Xiaokai Ran <ran.xiaokai@....com.cn>
> Cc: Yang Yang <yang.yang29@....com.cn>
> Cc: Jiang Xuexin <jiang.xuexin@....com.cn>
> Cc: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> Cc: David Hildenbrand <david@...hat.com>
> Signed-off-by: xu xin <xu.xin16@....com.cn>
> ---
>  Documentation/admin-guide/mm/ksm.rst | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/admin-guide/mm/ksm.rst b/Documentation/admin-guide/mm/ksm.rst
> index fb6ba2002a4b..f160f9487a90 100644
> --- a/Documentation/admin-guide/mm/ksm.rst
> +++ b/Documentation/admin-guide/mm/ksm.rst
> @@ -173,6 +173,13 @@ stable_node_chains
>          the number of KSM pages that hit the ``max_page_sharing`` limit
>  stable_node_dups
>          number of duplicated KSM pages
> +zero_pages_sharing
> +        how many empty pages are sharing kernel zero page(s) instead of

how many empty pages are sharing the kernel zero page(s) instead of
other user pages as it would happen normally. Only meaningful when
``use_zero_pages`` is enabled.

> +        with each other as it would happen normally. Only effective when
> +        enabling ``use_zero_pages`` knob.
> +
> +When enabling ``use_zero_pages``, the sum of ``pages_sharing`` +

When ``use_zero_pages`` is enabled, the sum of ``pages_sharing`` +

> +``zero_pages_sharing`` represents how much really saved by KSM.

``zero_pages_sharing`` represents the actual number of pages saved
by KSM.

> 
>  A high ratio of ``pages_sharing`` to ``pages_shared`` indicates good
>  sharing, but a high ratio of ``pages_unshared`` to ``pages_sharing``