linux-kernel - RE: [PATCH 0/8] memblock: introduce memsize showing reserved memory

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Date:   Wed, 30 Mar 2022 16:22:30 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     Mike Rapoport <rppt@...nel.org>
CC:     "vbabka@...e.cz" <vbabka@...e.cz>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        YongTaek Lee <ytk.lee@...sung.com>,
        "jaewon31.kim@...il.com" <jaewon31.kim@...il.com>
Subject: RE: [PATCH 0/8] memblock: introduce memsize showing reserved memory

>Hi,
>
>On Tue, Mar 29, 2022 at 11:46:20AM +0900, Jaewon Kim wrote:
>> >> > 
>> >> >I'm still not following. The reserved region sizes are available in the
>> >> >existing memblock debugfs.
>> >> >Why the names are important? What is the value of having names for *some*
>> >> >of the reserved regions?
>> >> 
>> >> Hi
>> >> 
>> >> There are many memory regions in memblock debugfs memory/reserved, and some might
>> >> be splited or merged with other region. Among regions in debugfs, we can't find 
>> >> the one we defined in device tree. Especially it is difficult to find the region we
>> >> described size only without start address.
>> >> 
>> >> On mobile environment, memory is used by not only CPU but also GPU, Camera, Secure
>> >> world, Audio, ETC. To support them, there are many reserved regions described in
>> >> device tree. So the name is quite important to recognize a region. And with thename
>> >> we can compare reserved memory map with other map.
>> >
>> >You still didn't describe your use case. What is the problem your patches
>> >are trying to solve? Why is it important to know what is the use of particular
>> >reserved region? 
>> >
>> >You propose complex mechanism that seems to fit very particular scenario
>> >and sprinkle some calls to this mechanism at random places because you need
>> >to "compare reserved memory map with other map".
>> >
>> >Does not sound convincing to me, sorry.
>> 
>> As I said serveral times, I want a simple knob showing all reserved
>> memory status.  The current debugfs, device tree do not show all those
>> information I want. I think you also know that.  i.e. late freed pages,
>> splited or merged memblock, address defined at boot time, kernel size,
>> ETC. 
>
>I know that there is not much information about reserved memory exposed and
>I understand *what* are you trying to achieve. But you never provided
>details about *why* you want this information exposed.
>
>I don't mind providing more visibility into reserved memory attributes in
>general, but I'd like to see something way more simple and localized.
>

I think the "what" is same as "why".
I want to look at all reservced memory status simply in a knob.

I also want to make in more simple and localized way, but there seems be
several ways to change reserved memory such as cmdline way, freeing after
boot, etc. I wanted to cover all those things.

That's OK. I hope someone later to try this again to show all the info.

>-- 
>Sincerely yours,
>Mike.