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Message-ID: <f15b0f64-5fa6-ac43-8299-4e48742c6243@bytedance.com>
Date:   Thu, 19 Oct 2023 16:17:48 +0800
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Subject: Re: [PATCH v2 0/2] handle memoryless nodes more appropriately
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To:     David Hildenbrand <david@redhat.com>
Cc:     akpm@linux-foundation.org, rppt@kernel.org, vbabka@suse.cz,
        mhocko@suse.com, willy@infradead.org, mgorman@techsingularity.net,
        mingo@kernel.org, aneesh.kumar@linux.ibm.com, ying.huang@intel.com,
        hannes@cmpxchg.org, osalvador@suse.de,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <cover.1697687357.git.zhengqi.arch@bytedance.com>
 <2a3bd858-5464-4569-be1e-2a1867d90c15@redhat.com>
From:   Qi Zheng <zhengqi.arch@bytedance.com>
In-Reply-To: <2a3bd858-5464-4569-be1e-2a1867d90c15@redhat.com>
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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