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

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Date:   Fri, 21 Oct 2022 12:18:10 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        xu xin <xu.xin.sc@...il.com>
Cc:     imbrenda@...ux.ibm.com, jiang.xuexin@....com.cn,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        ran.xiaokai@....com.cn, xu.xin16@....com.cn, yang.yang29@....com.cn
Subject: Re: [PATCH v3 0/5] ksm: support tracking KSM-placed zero-pages

On 19.10.22 00:54, Andrew Morton wrote:
> On Tue, 18 Oct 2022 09:00:22 +0000 xu xin <xu.xin.sc@...il.com> wrote:
> 
>>> 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.


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

-- 
Thanks,

David / dhildenb