linux-kernel - Re: [PATCH v2] hugetlb: simplify hugetlb handling in follow_page

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Date:   Tue, 6 Sep 2022 10:13:24 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        David Hildenbrand <david@...hat.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Michael Ellerman <mpe@...erman.id.au>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] hugetlb: simplify hugetlb handling in follow_page_mask

On 09/05/22 06:34, Christophe Leroy wrote:
> 
> 
> Le 02/09/2022 à 21:03, Mike Kravetz a écrit :
> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> > index fe4944f89d34..275e554dd365 100644
> > --- a/include/linux/hugetlb.h
> > +++ b/include/linux/hugetlb.h
> > @@ -264,6 +255,13 @@ static inline void adjust_range_if_pmd_sharing_possible(
> >   {
> >   }
> >   
> > +static inline struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma,
> > +				unsigned long address, unsigned int flags)
> > +{
> > +	WARN_ON_ONCE(1); /* should never be called if !CONFIG_HUGETLB_PAGE*/
> > +	return ERR_PTR(-EINVAL);
> 
> This function is called only when is_vm_hugetlb_page() is true.
> 
> When !CONFIG_HUGETLB_PAGE is_vm_hugetlb_page() always returns false, so 
> the call to hugetlb_follow_page_mask() should never be compiled in.
> 
> Use BUILD_BUG() to catch it at buildtime.
> 

Yes.  My bad as David suggested this previously.
How about we just leave out the function in the !CONFIG_HUGETLB_PAGE case?
We will get build errors without the need for a BUILD_BUG().

> > +}
> > +
> >   static inline long follow_hugetlb_page(struct mm_struct *mm,
> >   			struct vm_area_struct *vma, struct page **pages,
> >   			struct vm_area_struct **vmas, unsigned long *position,

-- 
Mike Kravetz