linux-kernel - Re: [PATCH 0/2] handle memoryless nodes more appropriately

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Message-ID: <3426457c-99bf-9f7c-f663-c29474d9fa73@bytedance.com>
Date:   Thu, 16 Feb 2023 07:11:19 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     akpm@...ux-foundation.org, vbabka@...e.cz, david@...hat.com,
        rppt@...nel.org, willy@...radead.org, mgorman@...hsingularity.net,
        osalvador@...e.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Muchun Song <muchun.song@...ux.dev>
Subject: Re: [PATCH 0/2] handle memoryless nodes more appropriately

On 2023/2/16 00:36, Michal Hocko wrote:
> On Wed 15-02-23 23:24:10, Qi Zheng wrote:
>> Hi all,
>>
>> Currently, in the process of initialization or offline memory, memoryless
>> nodes will still be built into the fallback list of itself or other nodes.
>>
>> This is not what we expected, so this patch series removes memoryless
>> nodes from the fallback list entirely.
>>
>> Comments and suggestions are welcome.

Hi Michal,

> 
> This is a tricky area full of surprises and it is really easy to

Would you mind giving an example of a "new problem"?

> introduce new problems. What kind of problem/issue are you trying to
> solve/handle by these changes?

IIUC, I think there are two reasons:

Firstly, as mentioned in commit message, the memoryless node has no
memory to allocate (If it can be allocated, it may also cause the panic
I mentioned in [1]), so we should not continue to traverse it when
allocating memory at runtime, which will have a certain overhead.

Secondly, from the perspective of semantic correctness, why do we remove
the memoryless node from the fallback list of other normal nodes
(N_MEMORY), but not from its own fallback list (PATCH[1/2])? Why should
an upcoming memoryless node continue exist in the fallback list of
itself and other normal nodes (PATCH[2/2])?

Please let me know if I missed something.

[1] 
https://lore.kernel.org/lkml/20230212110305.93670-1-zhengqi.arch@bytedance.com/

Thanks,
Qi

>