linux-kernel - Re: [PATCH] mm/hugetlb: Fix build failure with HUGETLB

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Date:   Tue, 17 Mar 2020 10:07:48 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Baoquan He <bhe@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Nishanth Aravamudan <nacc@...ibm.com>,
        Nick Piggin <npiggin@...e.de>, Adam Litke <agl@...ibm.com>,
        Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/hugetlb: Fix build failure with HUGETLB_PAGE but not
 HUGEBTLBFS

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