linux-kernel - Re: [PATCH 0/3] ksm: fix incorrect count of merged pages when enabling use_zero

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Message-ID: <20220929124242.60ef57ee@p-imbrenda>
Date:   Thu, 29 Sep 2022 12:42:42 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     xu.xin.sc@...il.com
Cc:     akpm@...ux-foundation.org, david@...hat.com,
        imbrenda@...ux.vnet.ibm.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, xu xin <xu.xin16@....com.cn>
Subject: Re: [PATCH 0/3] ksm: fix incorrect count of merged pages when
 enabling use_zero_pages

On Thu, 29 Sep 2022 02:52:06 +0000
xu.xin.sc@...il.com wrote:

> From: xu xin <xu.xin16@....com.cn>
> 
> Before enabling use_zero_pages by setting /sys/kernel/mm/ksm/
> use_zero_pages to 1, pages_sharing of KSM is basically accurate. But
> after enabling use_zero_pages, all empty pages that are merged with
> kernel zero page are not counted in pages_sharing or pages_shared.

that's because those pages are not shared between different processes.

> That is because the rmap_items of these ksm zero pages are not
> appended to The Stable Tree of KSM.
> 
> We need to add the count of empty pages to let users know how many empty
> pages are merged with kernel zero page(s).

why?

do you need to know how many untouched zero pages a process has?

does it make a difference if the zero page is really untouched or if it
was touched in the past but it is now zero?

> 
> Please see the subsequent patches for details.
> 
> 
> 
> 
> *** BLURB HERE ***
> 
> xu xin (3):
>   ksm: abstract the function try_to_get_old_rmap_item
>   ksm: add the accounting of zero pages merged by use_zero_pages
>   ksm: add zero_pages_merged in Documentation
> 
>  Documentation/admin-guide/mm/ksm.rst |  10 ++-
>  mm/ksm.c                             | 122 +++++++++++++++++++++------
>  2 files changed, 106 insertions(+), 26 deletions(-)
>