Re: [PATCH] mm, THP: vmf_insert_pfn_pud depends on CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD

[Alexandre Ghiti]

On 11/01/2018 11:06, Michal Hocko wrote:
> On Thu 11-01-18 09:53:31, Alexandre Ghiti wrote:
> > The only definition of vmf_insert_pfn_pud depends on
> > CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD being defined. Then its declaration in
> > include/linux/huge_mm.h should have the same restriction so that we do
> > not expose this function if CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD is
> > not defined.
> Why is this a problem? Compiler should simply throw away any
> declarations which are not used?
It is not a big problem but surrounding the declaration with the #ifdef 
makes the compilation of external modules fail with an "error: implicit 
declaration of function vmf_insert_pfn_pud" if 
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD is not defined. I think it is 
cleaner than generating a .ko which would not load anyway.

> > Signed-off-by: Alexandre Ghiti <aghiti@xxxxxxxxx>
> > ---
> >   include/linux/huge_mm.h | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index a8a1262..11794f6a 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -48,8 +48,10 @@ extern int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> >   			int prot_numa);
> >   int vmf_insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
> >   			pmd_t *pmd, pfn_t pfn, bool write);
> > +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> >   int vmf_insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr,
> >   			pud_t *pud, pfn_t pfn, bool write);
> > +#endif
> >   enum transparent_hugepage_flag {
> >   	TRANSPARENT_HUGEPAGE_FLAG,
> >   	TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
> > --
> > 2.1.4