linux-kernel - Re: [PATCH v8 2/6] ksm: count all zero pages placed by KSM

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Date:   Tue, 23 May 2023 11:51:09 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Yang Yang <yang.yang29@....com.cn>, akpm@...ux-foundation.org
Cc:     imbrenda@...ux.ibm.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 v8 2/6] ksm: count all zero pages placed by KSM

On 22.05.23 12:52, Yang Yang wrote:
> From: xu xin <xu.xin16@....com.cn>
> 
> As pages_sharing and pages_shared don't include the number of zero pages
> merged by KSM, we cannot know how many pages are zero pages placed by KSM
> when enabling use_zero_pages, which leads to KSM not being transparent with
> all actual merged pages by KSM. In the early days of use_zero_pages,
> zero-pages was unable to get unshared by the ways like MADV_UNMERGEABLE so
> it's hard to count how many times one of those zeropages was then unmerged.
> 
> But now, unsharing KSM-placed zero page accurately has been achieved, so we
> can easily count both how many times a page full of zeroes was merged with
> zero-page and how many times one of those pages was then unmerged. and so,
> it helps to estimate memory demands when each and every shared page could
> get unshared.
> 
> So we add ksm_zero_pages under /sys/kernel/mm/ksm/ to show the number
> of all zero pages placed by KSM.
> 
> v7->v8:
> Handle the case when khugepaged replaces a shared zeropage by a THP.
> 

Oh, and just a note, such version comments should go below the "--", 
such that they will automatically get dropped when applying the patch.

(Usually, version information in the cover letter is sufficient :) )

-- 
Thanks,

David / dhildenb