linux-kernel - Re: [RFC PATCH V1 0/3] mm/damon: Add CMA minotor support

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Date:   Fri, 18 Mar 2022 13:13:12 +0800
From:   xhao@...ux.alibaba.com
To:     David Hildenbrand <david@...hat.com>, sj@...nel.org
Cc:     rongwei.wang@...ux.alibaba.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        SeongJae Park <sj@...nel.org>
Subject: Re: [RFC PATCH V1 0/3] mm/damon: Add CMA minotor support


On 3/18/22 12:42 AM, David Hildenbrand wrote:
> On 17.03.22 08:03, Xin Hao wrote:
>> Hi David,
>>
>> On 3/16/22 11:09 PM, David Hildenbrand wrote:
>>> On 15.03.22 17:37, Xin Hao wrote:
>>>
>>> s/minotor/monitor/
>> Thanks,  i will fix it.
>>>> The purpose of these patches is to add CMA memory monitoring function.
>>>> In some memory tight scenarios, it will be a good choice to release more
>>>> memory by monitoring the CMA memory.
>>> I'm sorry, but it's hard to figure out what the target use case should
>>> be. Who will release CMA memory and how? Who will monitor that? What are
>>> the "some memory tight scenarios"? What's the overall design goal?
>> I may not be describing exactly what  i mean，My intention is to find out
>> how much of the reserved CMA space is actually used and which is unused,
>> For those that are not used, I understand that they can be released by
>> cma_release(). Of course, This is just a little personal thought that I
>> think is helpful for saving memory.
> Hm, not quite. We can place movable allocations on cma areas, to be
> migrated away once required for allocations via CMA. So just looking at
> the pages allocated within a CMA area doesn't really tell you what's
> actually going on.

I don't think so,  the damon not looking at the pages allocate, It is 
constantly monitoring who is using CMA area pages through tracking page 
access bit

in the kernel via the kdamond.x thread, So through damon, it can tell us 
about  the hot and cold distribution of CMA memory.

--cc  SeongJae Park <sj@...nel.org>


More about damon, you can refer to this 
link：https://sjp38.github.io/post/damon/ 
<https://sjp38.github.io/post/damon/>

>
-- 
Best Regards!
Xin Hao