linux-kernel - Re: [PATCH v2 0/2] handle memoryless nodes more appropriately

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Date:   Thu, 19 Oct 2023 16:17:48 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     akpm@...ux-foundation.org, rppt@...nel.org, vbabka@...e.cz,
        mhocko@...e.com, willy@...radead.org, mgorman@...hsingularity.net,
        mingo@...nel.org, aneesh.kumar@...ux.ibm.com, ying.huang@...el.com,
        hannes@...xchg.org, osalvador@...e.de,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 0/2] handle memoryless nodes more appropriately

Hi David,

On 2023/10/19 15:56, David Hildenbrand wrote:
> On 19.10.23 09:36, 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.
> 
> What's the end result of this change -- IOW why do we care? Patch #1 
> mentions "which will reduce runtime overhead." and patch #2 mentions 
> "This will incur some runtime overhead.". IIUC the comment in patch #1 
> correctly, these changes don't fix anything, correct?

Yes, after dropping the NODE_MIN_SIZE constrain in x86, the panic
problem fixed by this patch no longer exists (Unless there are other
architectures that have this constrain).

The reason I am re-sending this patch is that I agree with Ingo's point
of view:

```
While I agree with dropping the limitation, and I agree that
9391a3f9c7f1 should have provided more of a justification, I believe a
core MM fix is in order as well, for it to not crash.
```

I also think that core MM should be safe (not crash) even in some weird
topology.

> 
> Did you look into showing a performance gain?
> 

No, and I think the performance gain should be small, after all it just
traverses one less node. ;)

Thanks,
Qi