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

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Message-ID: <20220327135347epcms1p13faf0f2b7d98d3b59b25e903678d9c48@epcms1p1>
Date:   Sun, 27 Mar 2022 22:53:47 +0900
From:   Jaewon Kim <jaewon31.kim@...sung.com>
To:     Mike Rapoport <rppt@...nel.org>,
        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

> 
> 
>--------- Original Message ---------
>Sender : Mike Rapoport <rppt@...nel.org>
>Date : 2022-03-27 16:40 (GMT+9)
>Title : Re: [PATCH 0/8] memblock: introduce memsize showing reserved memory
> 
>Hi,
> 
>On Fri, Mar 25, 2022 at 05:38:46PM +0900, Jaewon Kim wrote:
> 
>> >--------- Original Message ---------
>> >Sender : Mike Rapoport <rppt@...nel.org>
>> >Date : 2022-03-25 16:46 (GMT+9)
>> >Title : Re: [PATCH 0/8] memblock: introduce memsize showing reserved memory
>> > 
>> >Hi,
>> > 
>> >On Thu, Mar 24, 2022 at 04:01:50PM +0900, Jaewon Kim wrote:
>> >> Some of memory regions can be reserved for a specific purpose. They are
>> >> usually defined through reserved-memory in device tree. If only size
>> >> without address is specified in device tree, the address of the region
>> >> will be determined at boot time.
>> >> 
>> >> We may find the address of the memory regions through booting log, but
>> >> it does not show all. And it could be hard to catch the very beginning
>> >> log. The memblock_dump_all shows all memblock status but it does not
>> >> show region name and its information is difficult to summarize.
>> >> 
>> >> This patch introduce a debugfs node, memblock/memsize, to see reserved
>> >> memory easily.
>> >> 
>> >> Here's an example
>> >> 
>> >> $ cat debugfs/memblock/memsize
>> >> 0x0f9000000-0x0fb000000 0x02000000 (   32768 KB )   map reusable linux,cma
>> >> 0x0b1900000-0x0b1b00000 0x00200000 (    2048 KB ) nomap unusable test1
>> >> 0x0b0200000-0x0b0400000 0x00200000 (    2048 KB )   map unusable test2
>> >>  (snipped)
>> >> 
>> >> Reserved    :  746924 KB
>> >>  .kernel    :  137027 KB
>> >>   .text     :   28158 KB
>> >>   .rwdata   :    3238 KB
>> >>   .rodata   :   13468 KB
>> >>   .bss      :   12570 KB
>> >>   .etc      :   79593 KB
>> >>  .unusable  :  609897 KB
>> >> System      : 3447380 KB
>> >>  .common    : 3152468 KB
>> >>  .reusable  :  294912 KB
>> >> Total       : 4194304 KB (  4096.00 MB )
>> > 
>> >Most of this information information is already available at various
>> >places, like the existing memblock debugfs, /proc/iomem and DT sysfs.
>> > 
>> >I don't see why we need yet another debugfs file to expose it.
>> 
>> Hi.
>> Thank you for your reply.
>> 
>> I don't think existing memblock debugfs or /proc/iomem shows information I want.
>> They don't show name and actually allocated address and size. And it does not
>> handle pages freed to buddy allocator after boot.
>> 
>> And which DT sysfs do you mean? If it is /proc/device-tree/reserved-memory, it
>> shows name and size, but it does not show address for only size defined regions.
>> It does not recognize the freed pages, either.
>> 
>> Especially I'd like to create a node showing all reserved memory status, their 
>> total size is same as the physical memory size. This was very useful when I 
>> compare reserved memory and kernel init time memory between different chipsets,
>> or between different sw release versions.
> 
>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.

Additionally as I said, we need one simple knob to look overall reservecd memory
status.

Thank you
Jaewon Kim

> 
>> Thank you
>> Jaewon Kim
> 
>-- 
>Sincerely yours,
>Mike.
>