linux-kernel - Re:[PATCH v3 0/5] ksm: support tracking KSM-placed zero-pages

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Date:   Mon, 24 Oct 2022 03:07:41 +0000
From:   xu xin <xu.xin.sc@...il.com>
To:     david@...hat.com
Cc:     akpm@...ux-foundation.org, 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 v3 0/5] ksm: support tracking KSM-placed zero-pages

>
>>>> A full description of the real-world end-user operational benefits of
>>>> these changes would help, please.
>>>>
>>>
>>> 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.
>> 
>> OK, thanks.
>> 
>>> The motivation for me to do this is that when I do
>>> an application optimization of KSM on embedded Linux for 5G platform, I find
>>> that ksm_merging_pages of some process becomes very small(but used to be large),
>>> which led me to think that there was any problem with the application KSM-madvise
>>> strategy, but in fact, it was only because use_zero_pages is on.
>> 
>> Please expand on the above motivation and experience, and include it in
>> the [0/n] changelog.  But let's leave it a few days to see if there's
>> additional reviewer input.
>> 
>
>I just posted a selftest:
>
>https://lore.kernel.org/all/20221021101141.84170-5-david@redhat.com/T/#u
>
>That could (should) be extended to test if unmerging works as expected.
>

Yes. As you said, these selftests can be extended to test if unsharing KSM-placed
zero pages works as expected, and I'm happy to do the extending after they are merged.

>
>Having that said, I think we really want a second pair of (KSM-expert) 
>eyes on these changes before moving forward with them.

OK, don't worry. Let it be reviewed for a more time, so as to absorb more views later.
If necessary, I will resend the patches to adjust to break_ksm()'s changes.