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Subject: Re: [PATCH] mm/hugetlb: Fix build failure with HUGETLB_PAGE but not
 HUGEBTLBFS
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Baoquan He <bhe@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Nishanth Aravamudan <nacc@us.ibm.com>,
        Nick Piggin <npiggin@suse.de>, Adam Litke <agl@us.ibm.com>,
        Andi Kleen <ak@suse.de>, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org
References: <7e8c3a3c9a587b9cd8a2f146df32a421b961f3a2.1584432148.git.christophe.leroy@c-s.fr>
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 <a31c86c9-2f86-4f40-a367-5953037ee137@oracle.com>
 <ff480af2-d376-3b99-ba9e-36397ecde232@c-s.fr>
From:   Mike Kravetz <mike.kravetz@oracle.com>
Message-ID: <dae98f9c-9233-a5b8-a824-1a26c7ad9e48@oracle.com>
Date:   Tue, 17 Mar 2020 10:07:48 -0700
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On 3/17/20 9:47 AM, Christophe Leroy wrote:
> 
> 
> Le 17/03/2020 à 17:40, Mike Kravetz a écrit :
>> On 3/17/20 1:43 AM, Christophe Leroy wrote:
>>>
>>>
>>> Le 17/03/2020 à 09:25, Baoquan He a écrit :
>>>> On 03/17/20 at 08:04am, Christophe Leroy wrote:
>>>>> When CONFIG_HUGETLB_PAGE is set but not CONFIG_HUGETLBFS, the
>>>>> following build failure is encoutered:
>>>>
>>>>   From the definition of HUGETLB_PAGE, isn't it relying on HUGETLBFS?
>>>> I could misunderstand the def_bool, please correct me if I am wrong.
>>>
>>> AFAIU, it means that HUGETLBFS rely on HUGETLB_PAGE, by default HUGETLB_PAGE is not selected when HUGETLBFS is not. But it is still possible for an arch to select HUGETLB_PAGE without selecting HUGETLBFS when it uses huge pages for other purpose than hugetlb file system.
>>>
>>
>> Hi Christophe,
>>
>> Do you actually have a use case/example of using hugetlb pages without
>> hugetlbfs?  I can understand that there are some use cases which never
>> use the filesystem interface.  However, hugetlb support is so intertwined
>> with hugetlbfs, I am thinking there would be issues trying to use them
>> separately.  I will look into this further.
>>
> 
> Hi Mike,
> 
> Series https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=164620
> 
> And especially patch 39 to 41.
> 

Ah, ok.  You are simply using a few interfaces in the hugetlb header files.
The huge pages created in your mappings are not PageHuge() pages.

-- 
Mike Kravetz