Re: [PATCHv2, RFC 07/30] thp, mm: introduce mapping_can_have_hugepages()predicate

[Ric Mason]

On 04/05/2013 11:45 AM, Ric Mason wrote:
> Hi Kirill,
> On 03/15/2013 01:50 AM, Kirill A. Shutemov wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> >
> > Returns true if mapping can have huge pages. Just check for __GFP_COMP
> > in gfp mask of the mapping for now.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > ---
> >   include/linux/pagemap.h |   10 ++++++++++
> >   1 file changed, 10 insertions(+)
> >
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index e3dea75..3521b0d 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -84,6 +84,16 @@ static inline void mapping_set_gfp_mask(struct 
> > address_space *m, gfp_t mask)
> >                   (__force unsigned long)mask;
> >   }
> >   +static inline bool mapping_can_have_hugepages(struct address_space 
> > *m)
> > +{
> > +    if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
> > +        gfp_t gfp_mask = mapping_gfp_mask(m);
> > +        return !!(gfp_mask & __GFP_COMP);
>
> I always see !! in kernel, but why check directly instead of have !! 
> prefix?

s/why/why not

> > +    }
> > +
> > +    return false;
> > +}
> > +
> >   /*
> >    * The page cache can done in larger chunks than
> >    * one page, because it allows for more efficient

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