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

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Message-ID: <a31c86c9-2f86-4f40-a367-5953037ee137@oracle.com>
Date:   Tue, 17 Mar 2020 09:40:06 -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 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.

-- 
Mike Kravetz