linux-kernel - Re: [PATCH v6 0/6] ksm: support tracking KSM-placed zero-pages

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Date:   Fri, 14 Apr 2023 09:35:07 +0800
From:   xu xin <xu.xin.sc@...il.com>
To:     akpm@...ux-foundation.org
Cc:     david@...hat.com, 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,
        yang.yang29@....com.cn
Subject: Re: [PATCH v6 0/6] ksm: support tracking KSM-placed zero-pages

>> The core idea of this patch set is to enable users to perceive the number of any
>> pages merged by KSM, regardless of whether use_zero_page switch has been turned
>> on, so that users can know how much free memory increase is really due to their>
>> madvise(MERGEABLE) actions. But the problem is, when enabling use_zero_pages,
>> all empty pages will be merged with kernel zero pages instead of with each
>> other as use_zero_pages is disabled, and then these zero-pages are no longer
>> monitored by KSM.
>

We have sent the v7 series, so some old codes might be changed, and no need to talk
more.

>We appear to have some outstanding activity on this quite old patchset.
>>From my notes:
>
>- An unresponded-to question from Claudia:
>	https://lkml.kernel.org/r/20230307192421.30ab869c@p-imbrenda
>

Claudia is right, but the v7 patches don't rely on rmap_items now, so we can skip
this comment.

>- Hoping for overall review from David
>

David's review is great, and we accept his advice on the basic approach in v7 patches
to track the ksm zero pages. and now the v7 patches use pte_dirty to mark the
KSM-placed zere pages. But since pte_dirty is related to architectures, and some
architecture may treat pte_dirty as writable, so we restrict the feature of tracking
ksm zero pages only to the tested and well-working architecture.

>- Another query from Claudia, and a response indicating that a v7 is
>  in the works.
>	https://lore.kernel.org/all/20230307194320.79373a26@p-imbrenda/T/#u

The v7 series don't changed it there now, then we can skip it.

>
>- Another unresponded-to review query:
>	https://lkml.kernel.org/r/20230307195119.745d0b46@p-imbrenda
>

The v7 series have referred to Claudia's review but made a few modifications.

>- Another response indicating that a v7 is coming
>	https://lkml.kernel.org/r/20230307195313.2e21245a@p-imbrenda
>
> So I think I'll drop the v6 series.  Please address all these things in
> the next version and let's start over.

Yes, the next version is here:
https://lore.kernel.org/lkml/202304131346489021903@zte.com.cn/