linux-kernel - Re: [PATCH RFC 1/4] drivers/base/node: Add demotion

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Fri, 02 Feb 2024 16:19:56 +0800
From: "Huang, Ying" <ying.huang@...el.com>
To: "Zhijian Li (Fujitsu)" <lizhijian@...itsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,  Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>,  "rafael@...nel.org" <rafael@...nel.org>,
  "linux-mm@...ck.org" <linux-mm@...ck.org>,  "Yasunori Gotou (Fujitsu)"
 <y-goto@...itsu.com>,  "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>,  Jagdish Gediya <jvgediya@...ux.ibm.com>
Subject: Re: [PATCH RFC 1/4] drivers/base/node: Add demotion_nodes sys
 infterface

"Zhijian Li (Fujitsu)" <lizhijian@...itsu.com> writes:

> On 31/01/2024 11:17, Li Zhijian wrote:
>>>> node[0].preferred = 2
>>>> node[0].demotion_targets = 2-5
>>>> node[1].preferred = 5
>>>> node[1].demotion_targets = 2-5
>>>> node[2].preferred = 4
>>>> node[2].demotion_targets = 3-4
>>>> node[3].preferred = <empty>
>>>> node[3].demotion_targets = <empty>
>>>> node[4].preferred = <empty>
>>>> node[4].demotion_targets = <empty>
>>>> node[5].preferred = 3
>>>> node[5].demotion_targets = 3-4
>>>>                                                                           But
>>>> this demotion path is not explicitly known to administrator. And with
>>>> the
>>>> feedback from our customers, they also think it is helpful to know demotion
>>>> path built by kernel to understand the demotion behaviors.
>>>>
>>>> So i think we should have 2 new interfaces for each node:
>>>>
>
>>>> /sys/devices/system/node/nodeN/demotion_allowed_nodes
>>>> /sys/devices/system/node/nodeN/demotion_preferred_nodes
>>>>
>>>> I value your opinion, and I'd like to know what you think about...
>>>
>>> Per my understanding, we will not expose everything inside kernel to
>>> user space.  For page placement in a tiered memory system, demotion is
>>> just a part of the story.  For example, if the DRAM of a system becomes
>>> full, new page allocation will fall back to the CXL memory.  Have we
>>> exposed the default page allocation fallback order to user space?
>
>
> Back to our initial requirement:
> When demotion is enabled, what's the demotion path, especially the preferred node?
> are they consistent with administrator's expectations?"
>
> It seems there is no a direct answer. But actually, kernel have already known
> this information, IMHO, exposing them to users is not a bad choice.
>
> This information is able to help them adjust/tune the machine before really
> deploy their workloads.
>
> If the sysfs approach isn't better enough, is it possible to have another more
> user-friendly way to convey this information? like the allocation fallback order does,
> simply print them to dmesg?

I have no object to print some demotion information in dmesg.

--
Best Regards,
Huang, Ying

>
>> 
>> Good question, I have no answer yet, but I think we can get the fallback order
>> from the dmesg now.
>> 
>> The further action for us is that we will also try improve the use space tool,
>> such as numactl to show the demotion path with the help of this exposed information.