linux-kernel - Re: [PATCH v4] hugetlb: Fix wrong use of nr_online

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Message-ID: <ecd49289-383d-7a6a-d3be-168bdebc9ebc@huawei.com>
Date:   Wed, 20 Apr 2022 14:17:34 +0800
From:   "liupeng (DM)" <liupeng256@...wei.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     <mike.kravetz@...cle.com>, <david@...hat.com>,
        <yaozhenguo1@...il.com>, <baolin.wang@...ux.alibaba.com>,
        <songmuchun@...edance.com>, <liuyuntao10@...wei.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <dave@...olabs.net>
Subject: Re: [PATCH v4] hugetlb: Fix wrong use of nr_online_nodes


On 2022/4/19 22:07, Kefeng Wang wrote:
>
> On 2022/4/19 12:03, Andrew Morton wrote:
>> On Sat, 16 Apr 2022 10:35:26 +0000 Peng Liu <liupeng256@...wei.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.
>
Thanks, you are right.

I have constructed node =0, 1, 3, 4, and requested huge pages as:

hugepagesz=1G hugepages=0:1,4:1 hugepagesz=2M hugepages=0:1024,4:1024

Without this patch:

  HugeTLB: Invalid hugepages parameter 4:1
  HugeTLB: Invalid hugepages parameter 4:1024
  HugeTLB registered 1.00 GiB page size, pre-allocated 0 pages
  HugeTLB registered 2.00 MiB page size, pre-allocated 1024 pages

With this patch:

   HugeTLB registered 1.00 GiB page size, pre-allocated 2 pages
   HugeTLB registered 2.00 MiB page size, pre-allocated 2048 pages

>> .
> .