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Subject: Re: [PATCH v4] hugetlb: Fix wrong use of nr_online_nodes
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To:     Andrew Morton <akpm@linux-foundation.org>,
        Peng Liu <liupeng256@huawei.com>
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On 2022/4/19 12:03, Andrew Morton wrote:
> On Sat, 16 Apr 2022 10:35:26 +0000 Peng Liu <liupeng256@huawei.com> wrote:
>
>> Certain systems are designed to have sparse/discontiguous nodes. In
>> this case, nr_online_nodes can not be used to walk through numa node.
>> Also, a valid node may be greater than nr_online_nodes.
>>
>> However, in hugetlb, it is assumed that nodes are contiguous. Recheck
>> all the places that use nr_online_nodes, and repair them one by one.
> oops.
>
> What are the user-visible runtime effects of this flaw?

For example, there are four node=0,1,2,3, and nid = 1 is offline 
node，nr_online_nodes = 3

1) per-node alloc (hugepages=1:2) fails,

2) per-node alloc (hugepages=3:2) fails, but it could succeed.

I assume that there is no user-visible runtime effects.

> .