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

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Message-ID: <YkQB6Ah603yPR3qf@kernel.org>
Date:   Wed, 30 Mar 2022 10:08:24 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Jaewon Kim <jaewon31.kim@...sung.com>
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.

-- 
Sincerely yours,
Mike.