linux-kernel - Re: [POC] Extend "movable_node" to "movable_node=nn@ss" and add the interface in /sys to show the value

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Date:   Wed, 11 Oct 2017 15:55:13 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-acpi@...r.kernel.org, hpa@...or.com, tglx@...utronix.de,
        mingo@...hat.com, keescook@...omium.org, arnd@...db.de,
        dyoung@...hat.com, dave.jiang@...el.com, lv.zheng@...el.com,
        rjw@...ysocki.net, yasu.isimatu@...il.com,
        caoj.fnst@...fujitsu.com, lizhijian@...fujitsu.com
Subject: Re: [POC] Extend "movable_node" to "movable_node=nn@ss" and add the
 interface in /sys to show the value

Hi Fan San,

On 10/11/17 at 10:28am, Chao Fan wrote:
> Hi all,
> 
> Here is a problem:
> Here is a machine with several NUMA nodes and some of them are hot-pluggable,
> It's not good for kernel to be extracted in the memory region of movable node.
> But in current code, I print the address choosen by kaslr and found it may be
> placed in movable node sometimes. To solve this problem, it's better to the
> memory region choosen by kaslr to immovable node in kaslr.c. But the memory
> infomation about if it's hot-pluggable is stored in ACPI SRAT table, which is
> parsed after kernel is extracted. So we can't get the detail memory infomation
> before extracting kernel.
> 
> There are two methods to solve this problem:
> 
> 1. Get and parse the srat table before kernel extracted, then mark the memory
>    region in movable node which should be avoided in kaslr.
>    I have send the patch:
>    https://www.spinics.net/lists/kernel/msg2595546.html
>    But the change is large and then here is the second method.
> 
> 2. Extend the movable_node to movable_node=nn@ss, in which nn means
>    the size of memory in immovable node, and ss means the start position of
>    this memory region.
>    But it brings another question, it may be a little difficult for a normal
>    user to specify the nn and ss. Because it's hard for a user to know the value
>    of the memory in immovable node.
>    So I wonder if it's good to add a interface in /sys, like:
>    # cat /sys/device/system/memory/immovable_node

You can post patch. By the way, can the existing
/sys/devices/system/memory/memoryX/removable be used instead?

Thanks
Baoquan

>    nn@ss
>    nn@ss
>    ...
>    to show the two value.
>    When srat table is parsed in acpi_parse_memory_affinity, fill the value
>    and user can get and use them.
> 
> If anyone has a better method, please let me know.
> Any comments will be welcome.
> 
> Thanks,
> Chao Fan
> 
>